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Choosing the right main contractor for your building project is probably the most important decision you’ll make. Get it right and your project runs smoothly, finishes on time, and gives you the home you dreamed of. Get it wrong and you’re looking at delays, cost overruns, poor workmanship, and months of stress. I’ve watched too many Manchester homeowners rush into hiring a contractor based on a cheap quote or a friendly chat, only to regret it later. The interview stage is your chance to separate the professionals from the cowboys, and the questions you ask matter. This guide gives you the exact questions to ask potential contractors, what answers you should be looking for, and how to spot red flags before it’s too late.
Most people spend more time researching which TV to buy than which contractor to hire for a £100,000 extension. That’s backwards. Your contractor will be working on your biggest asset, your home, for months. They’ll have access to your property, control over your money, and responsibility for meeting building regulations and safety standards. A bad contractor can bankrupt you, leave you with a dangerous structure, or disappear halfway through leaving you with an unfinished mess.
The interview is your chance to assess whether this person or company is professional, experienced, financially stable, and someone you can work with for the duration of your project. It’s also when you check their insurance, references, and previous work. Don’t just accept what they tell you. Ask for proof. A good contractor will expect these questions and have answers ready. If someone gets defensive or evasive when you ask basic questions, that’s a massive red flag. Walk away.
Before you start interviewing contractors, do your homework. Have your plans and specifications ready so you’re comparing like for like. Know your budget and timeline. Make a list of your priorities and any particular concerns. Prepare the same set of questions for each contractor so you can compare answers fairly. Take notes during each interview or record it with their permission. Don’t rely on memory because you’ll forget details later.
Schedule enough time for each interview, at least an hour. Meet them at your property so they can see the site and you can see how they interact with the space. If they’re rushing off to another meeting or seem distracted, that’s how they’ll be during your project too. Bring your partner or a trusted friend so you have a second opinion. Sometimes other people spot things you miss. Most importantly, trust your gut. If something feels off, even if you can’t put your finger on it, take that seriously.
Here are the questions that separate good contractors from bad ones. Ask them all.
You need to know whether you’re dealing with a sole trader, a partnership, or a limited company. Limited companies offer you more protection because the company is a legal entity separate from the person. If they go bust, you might have some recourse. Ask how long they’ve been in business and where they’re based. A contractor who’s been trading successfully in Manchester for ten years is a much safer bet than someone who set up last month. Check their details on Companies House if they’re a limited company. Look for any previous company names or insolvencies.
This is non-negotiable. Every contractor must have public liability insurance, usually for at least £2 million, which covers damage to your property or injury to third parties. If they employ people, they need employers’ liability insurance too. Professional indemnity insurance is also good because it covers design errors if they’re doing design and build. Don’t just take their word for it. Ask to see current insurance certificates and check the expiry dates. Some contractors let their insurance lapse to save money. If they’re not insured and something goes wrong, you could be liable.
Not all contractors are good at everything. Someone who builds apartment blocks might be terrible at domestic extensions. Ask specifically about projects similar to yours. How many loft conversions have they done in Manchester terraces? What’s the biggest extension they’ve managed? Do they have experience with listed buildings if yours is listed? Ask to see a portfolio of completed work and ideally visit a project that’s similar to what you want. If they can’t show you relevant experience, they’re learning on your job, which is risky and expensive.
Most main contractors use subcontractors for specialist trades like electrics, plumbing, and roofing. That’s fine and normal. What matters is whether they manage those subcontractors properly. Ask who they use for each trade and how long they’ve worked with them. Established relationships with reliable subcontractors are a good sign. Find out who’s responsible if a subcontractor messes up. The main contractor should take full responsibility, not pass the buck. Ask how they ensure subcontractors are properly qualified and insured. Cowboys often use unqualified mates to keep costs down.
You need to know if they’re going to prioritise your project or if you’ll be one of five jobs they’re juggling. Ask what projects they’re currently working on and when they expect to finish. Find out when they could start your project and whether they’ll be on site full-time or just visiting occasionally. If they can start tomorrow, be suspicious. Good contractors are usually booked up a few weeks or months in advance. If they’re managing multiple projects, how will they ensure yours doesn’t get neglected?
Get a realistic timeline from start to finish, broken down into stages. A typical single-storey extension in Manchester takes 12 to 16 weeks. A full house renovation might be 6 to 9 months. A new build could be 9 to 12 months. If they’re promising timelines that seem too good to be true, they probably are. Ask what could cause delays and how they manage them. Weather, material shortages, and planning issues all cause delays. A good contractor factors these into their timeline and communicates if things change.
Never accept a verbal quote or a figure scribbled on the back of an envelope. You need a detailed written quotation that breaks down labour, materials, and any other costs. It should specify exactly what’s included and what’s not. Ask about payment terms. How much deposit do they want and when are stage payments due? Be wary of anyone asking for a big upfront payment or demanding full payment before completion. A reasonable structure is 10 to 20 percent deposit, then payments at key stages like foundations complete, frame erected, first fix done, and so on.
You need to know who you’ll be dealing with day-to-day. Is it the owner, a project manager, or a site foreman? How will they keep you updated on progress? Will you get daily or weekly updates? How quickly do they respond to questions or concerns? Good communication prevents problems from escalating. If the person you’re interviewing won’t be your day-to-day contact, insist on meeting the person who will be before you sign anything.
Nearly every building project has some variation from the original plan. You might change your mind about something, or hidden problems might emerge once work starts. Ask how they manage these changes. Will you get a written quote for extras before work proceeds? How are variations priced and approved? Get this in writing in your contract so there are no surprises when they present you with a huge bill for extras at the end.
A contractor who stands behind their work will offer guarantees. Ask what warranty period they provide and what it covers. Typical warranties range from one to ten years depending on what it covers. Structural work should have longer warranties than decorative finishes. Check if the warranty is insurance-backed. If they go bust, an insurance-backed warranty means you can still claim. Some contractors are members of schemes like TrustMark or the Federation of Master Builders that offer warranty protection.
Every contractor should be able to give you contact details for at least three recent clients whose projects were similar to yours. Don’t just ask for references, actually contact them. Ask if the work was completed on time and on budget, if they’d hire this contractor again, how they handled problems, and if there were any issues after completion. If a contractor refuses to give references or makes excuses, walk away. Some contractors will only give you references for their best projects. Try to find some real reviews online from clients who weren’t handpicked.
Things go wrong on building projects. Materials arrive damaged, weather causes delays, or you disagree about something. Ask how they handle disputes and what their process is for resolving issues. Are they members of any trade body dispute resolution schemes? Do they have a formal complaints procedure? A contractor who gets defensive at this question probably doesn’t handle problems well. A good contractor will explain their process calmly and show you it’s in their contract.
Some warning signs should make you think twice or walk away completely. If they pressure you to sign immediately or say the quote is only valid for 24 hours, it’s a sales tactic. Good contractors don’t need to pressure you. If they want a large deposit upfront, more than 20 to 25 percent, or want payment in cash only, that’s dodgy. They might be hiding from HMRC or planning to take your money and run. If they can’t or won’t provide proof of insurance, references, or examples of previous work, don’t hire them.
Vague or verbal quotes with no written detail are a recipe for disputes later. If they’re not registered with Companies House and have no online presence, it’s hard to hold them accountable. If they bad-mouth other contractors or previous clients, they’ll probably bad-mouth you too. If they can’t answer basic questions about building regulations, planning permission, or how they’ll manage the project, they’re not qualified. Trust your instincts. If something feels wrong, it probably is.
Once you’ve interviewed several contractors, resist the temptation to just pick the cheapest. Price matters, but it’s not everything. A quote that’s significantly lower than others might mean the contractor has cut corners, missed things out, or is planning to hit you with extras later. Compare the detail in each quote. Do they all include the same things? Check their timelines, payment terms, warranties, and overall professionalism.
Think about who you’d actually want to work with for months. Who communicated well? Who seemed most professional and organised? Who had the best relevant experience? Sometimes it’s worth paying a bit more for a contractor you trust and who has a proven track record. The cheapest quote can end up being the most expensive if the job is done badly and you have to pay someone else to fix it.
After interviewing all your shortlisted contractors, sit down with your notes and compare them properly. Create a simple scoring system. Give each contractor marks out of ten for things like experience, communication, price, insurance, references, and gut feeling. This helps you see beyond just the price and make a balanced decision. Talk it through with your partner or anyone else involved in the decision.
Once you’ve chosen your contractor, don’t rush into signing. Read the contract thoroughly and get a solicitor to review it if it’s a big project. Make sure everything you discussed is actually in the written contract. If anything is missing or different from what was agreed, ask for it to be changed before you sign. Never feel pressured to sign something you’re not comfortable with. Once you’ve signed and paid a deposit, it’s much harder to back out.
After you’ve hired your contractor, set the relationship up for success from day one. Have a kick-off meeting before work starts to go through the schedule, how you’ll communicate, site access, where materials will be stored, working hours, and what to do if problems arise. Get mobile numbers for your main contact and theirs. Agree how often you’ll have progress meetings and how changes will be managed.
Keep records of everything throughout the project. Take photos at each stage. Keep copies of all emails, texts, and invoices. If the contractor asks for a change or variation, get it in writing with costs before agreeing. Pay stage payments when work is genuinely complete, not before. Hold back a retention of 5 to 10 percent until a few weeks after completion to make sure everything is finished properly. A good working relationship based on clear communication and mutual respect makes everything easier.
