The cheapest quote is rarely the cheapest build. When you're planning an extension or renovation, the builder you choose shapes everything that follows: how much you really spend, how long you live with the disruption, and how you feel at the end of it.
Most homeowners only go through this once or twice in their lives. You'll receive three or four quotes, each laid out differently, each with its own assumptions. The total at the bottom is the one number that looks easy to compare, so it's natural to lean on it. But price on its own tells you very little about what you'll actually get, or what the final bill will be.
This guide explains why quotes are so hard to compare, what's worth looking for beyond the headline figure, and the questions that help you find a builder you can genuinely rely on.
Why quotes are so hard to compare
Two quotes for the same drawings can differ by tens of thousands of pounds, and neither is necessarily wrong. They're usually pricing different things. The differences tend to hide in a few places:
What's included. One builder prices the kitchen fit, decorating and flooring; another stops at plastered walls. Unless you read line by line, you may not notice.
Provisional sums and PC sums. These are allowances for items not yet designed or chosen, such as a kitchen, sanitaryware or landscaping. A low allowance makes a quote look cheaper today and costs you later when the real choice is made.
Exclusions. Skip hire, scaffolding, building control fees, party wall matters, drainage and making good are common omissions. Each one becomes an extra.
Assumptions about the unknown. Foundations, existing structure and services can't always be fully known until work begins. A careful builder tells you where the risk sits; a less careful one leaves it out and hopes for the best.
Programme and resourcing. A quote that assumes a much shorter build may be relying on optimism rather than a plan.
Here's a simplified example of how two quotes for the same extension can look very different once you line them up:
| Item | Builder A | Builder B |
|---|---|---|
| Headline price | £78,000 | £92,000 |
| Kitchen allowance | £6,000 | £15,000 |
| Flooring and decoration | Excluded | Included |
| Scaffolding and skips | Excluded | Included |
| Groundworks risk | Not mentioned | Provisional sum with explanation |
| Programme | 10 weeks | 16 weeks, phased |
Illustrative figures only. On paper Builder A is £14,000 cheaper. Once a realistic kitchen, the excluded items and likely extras are added, the gap closes or reverses, and Builder B has told you far more about how the job will actually run.
The lesson isn't that higher is better. It's that a quote is only as useful as its clarity. If you can't tell what's in it, you can't compare it.
What actually matters beyond the price
Every builder you shortlist should be able to build well. That's the baseline, not the differentiator. What separates a good experience from a stressful one is how the project is managed, and how you're looked after along the way.
Predictability. You want to know what's happening, when, and what it will cost. That comes from planning: a realistic programme, a clear budget, and early warning when something changes. Surprises are where stress and overspend begin.
Systems and processes. Good intentions aren't enough on a live site. Ask how the builder tracks the programme, manages trades, records variations and keeps you updated. A builder with proper systems can show you, not just tell you.
Clear, honest communication. Most homeowners don't work in construction, and they shouldn't have to. A good builder explains decisions in plain language, gives you options rather than ultimatums, and is upfront when something isn't right.
Guidance and knowledge. You'll face dozens of decisions, from finishes to sequencing. A builder who understands design intent and can advise you, rather than simply waiting for instructions, saves you time, money and second-guessing.
Integrity and care. Ultimately you're inviting someone into your home for months. You need to trust that they'll treat it, and you, with respect, and that they'll do the right thing when no one is watching.
How to vet a builder: questions worth asking
Use these when you meet each builder. The answers, and how readily they're given, will tell you more than the quote.
About the quote
What exactly is included and excluded? Can you walk me through it line by line?
Which items are provisional or PC sums, and how did you arrive at those figures?
Where are the biggest risks on this job, and how have you allowed for them?
How are changes and variations priced and agreed before work goes ahead?
About how you run a project
Who will be my day-to-day contact, and how often will I hear from you?
How do you plan and track the programme? Can I see an example?
How do you manage subcontractors and the quality of their work?
What happens if something goes wrong or falls behind?
About your track record
Can I see similar projects you've completed recently?
Can I speak to two or three previous clients directly?
Do architects or designers regularly recommend you?
What insurance do you hold, and can I see the certificates?
A word on that architect question. Builders who are repeatedly invited to tender by architects have already been vetted by professionals who see their work up close. It's one of the most reliable signals you can get.
Red flags to watch for
A quote that's a single figure on one page, with little or no breakdown
A price far below the others, with no clear explanation of why
Vague answers about who will manage the site day to day
Pressure to sign quickly or pay a large deposit upfront
No written contract, or reluctance to put agreements in writing
Reluctance to put you in touch with past clients
A programme that seems too good to be true
None of these automatically rules a builder out, but each deserves a straight answer before you commit.
How we approach it at Saint Developments
We believe every contractor should build well. What we set out to offer on top of that is peace of mind: a project that's predictable, well managed and clearly explained from the first conversation to handover.
In practice, that means:
An early ballpark estimate, so you know whether your plans and budget are aligned before you spend more on design
A fixed cost with phased invoicing, so you know the price from the outset and pay in stages as each phase of work is completed, rather than in large lump sums
Transparent, itemised proposals, with allowances and assumptions set out in plain language
Proven systems and processes to plan the programme, manage trades and keep you informed throughout
Genuine care for your home, your time and your experience of the build
Much of our work comes through architects who invite us to tender on their residential projects. We take that trust seriously, and we bring the same standard to every homeowner we work with.
If you're comparing builders for an extension or renovation, we're always happy to talk it through, even if it's just to help you make sense of the quotes you already have.
Read more about Our Approach
Architects and designers: see For Architects
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