Why Your Builder’s ‘Rough Quote’ Might Be Thousands Off
(And What to Do Instead)
If you’ve ever asked a builder, “How much do you think this will cost?” and received a quick answer on the spot, you’re not alone. Early ballpark figures are common, but they’re rarely comprehensive — and without detailed plans, they can shift by hundreds of thousands as the design progresses.
At Whisker Architecture, we see this scenario regularly – and unfortunately, it's often the homeowner left feeling confused, misled, and overwhelmed.
This article explains why early feasibility quotes from builders are often inaccurate, how they differ from formal pricing, and what you can do to protect your project – and your budget.
What level of finish is being assumed?
What is a ‘rough quote’ – and how is it different from a formal builder quote?
Many homeowners don’t realise there’s a major difference between:
Early verbal estimates (often given during a casual site visit or design consultation), and
Detailed quotes provided by builders at the tender or contract stage, based on full documentation.
We’re not talking about the formal pricing builders provide after reviewing architectural drawings, engineering, specifications, and reports. That kind of quoting is rigorous and usually reliable.
Instead, this article focuses on the early-stage numbers that get thrown around before plans are finalised – the kind of ballpark figures that sound reassuring but can derail your project later.
Can I trust a builder’s early estimate?
Verbal or ballpark estimates are often based on memory, assumptions, or previous projects, rather than your site and brief. Builders are asked for these numbers every day, and it’s understandable that they keep things broad and optimistic at this stage. The risk for homeowners is that these numbers feel certain when they’re not.
Here’s one real example:
A client received a verbal estimate of $250,000 for a renovation extension. When we ran the project through our Home Masterplan Report process (including feasibility layouts and independent cost advice), the true cost was closer to $750,000. That’s a huge gap – and understandably, the client felt confused and disappointed.
Why do builder quotes and architect estimates differ so much in the early stages?
Because most architects approach feasibility differently.
At Whisker Architecture, we don’t rely on vague square metre rates. Our Home Masterplan Reports include:
A review of site and planning restrictions
Three tailored design options
Cost estimates from independent construction estimators (like ProCalc), based on real data from current builder tenders
These estimates are more aligned with final outcomes – because they’re built on a full scope, not assumptions.
In contrast, some builders may provide rough numbers without reviewing plans in detail or factoring in the entire project lifecycle.
This doesn’t make them dishonest – just early, broad, and often incomplete.
Builders are asked for quick prices on projects every day of the week - many of which the builder will never hear from again - so it’s no wonder they err on the side of optimism.
How much custom joinery is the builder assuming is included in those early figures?
We’ve seen what happens when expectations don’t align
Another example:
A client was verbally quoted $800,000 for a new build. By the time the project reached town planning, the budget had crept to $1.1 million + fees. By tender, it was likely to land near $1.3 million – exactly what we had originally advised based on the feasibility analysis.
Unfortunately, the client had already lost faith in our advice and stepped away, believing we had overestimated. The truth is, we had simply provided a realistic figure from the start – while others were still guessing.
Why are early builder estimates often too low?
Sometimes early figures are a way of keeping a project conversation moving, and sometimes they’re simply a reflection of habit. Either way, they tend to be optimistic and incomplete, which can create misaligned expectations and frustration down the track.
Common omissions in early quotes include:
Structural engineering
Window and glazing upgrades (especially if altering more than 50% of the building)
Flood level requirements
Demolition, site clearing, or tree removal
GST
Town planning requirements
Site access, soil class, or service connections
All of these are real costs that must be included in your project planning. If they’re not, the number you’re working with isn’t realistic.
Site Analysis
An accurate understanding of what’s required by statutory authorities could be the difference between allowing for all new windows to the house or letting that be a nasty surprise later.
When we launched in late 2020, we made this mistake too
In the early days, we too used square metre rates for early-stage budgeting – just like many others. But during the COVID construction boom, we learned quickly that the market shifts fast, and generalised cost data without site-specific context is risky.
At Whisker Architecture, we’ve moved away from vague square-metre rates.
Our Home Masterplan Reports include a review of planning restrictions, three tailored design options, and independent cost advice based on current builder tenders. These aren’t perfect forecasts — no estimate is — but they align with the level of detail, craftsmanship, and customisation our clients expect, and with the way builders ultimately price at tender.
How can I get accurate cost advice before I start designing?
If you’re planning a renovation, extension, or custom home in Victoria, the most reliable way to begin is with a pre-design feasibility service like our Home Masterplan Report.
This includes:
Site and council planning review
Three tailored design options
Independent cost estimates
Guidance on scope, staging, and budget strategy
This kind of early strategy work will help you avoid chasing the wrong budget – or worse, giving up on the project altogether after months of misalignment.
So who should I trust – my architect or my builder?
Ideally, both your architect and builder are part of the process.
In the early stages, architects can help align your brief, site, and budget so you’re set up for success. During documentation builders can provide excellent price and buildability feedback. Once full documentation is complete, builders are best placed to provide a detailed, reliable price. When each plays their part at the right stage, you get clarity from day one and confidence right through to construction.
But here’s where it’s important to dig a little deeper: not all architects approach cost planning the same way.
Some architects rely on rough square metre rates or base their advice on the last similar-sized project they completed. That might feel reassuring, but it doesn’t account for the specifics of your site, your local planning conditions, or current market volatility.
At Whisker Architecture, we take a different approach.
We use dedicated estimation software powered by independent cost consultants who specialise in real-time construction forecasting. This means you get realistic cost advice at the very beginning – before you fall in love with a design that may be double your budget.
If you’re comparing a casual verbal quote to a structured feasibility process backed by data, you’re not comparing like for like.
Ask questions. Look for clarity. And make sure whoever you trust is willing to tell you the truth – even if it’s not what you hoped to hear.
Need clarity from day one?
Book a free 20-minute Clarity Call with Audrey, or Download our guide: “Can I Afford My Dream Home?”
You’ll learn what costs to expect, how to plan with confidence, and whether your dream home is actually achievable.
Whisker Architecture – trusted by families across Victoria for tailored, sustainable design and honest advice.
As Home Architects in Melbourne work with Architectural Builders Melbourne, and Melbourne Custom Home Builders to deliver modern homes that reflect your values.
