Builders price what they can see. If a drawing set does not clearly show a detail, the builder has three choices: assume something, exclude it, or add a contingency. All three end up costing you money — either in the quoted figure, or later as a variation when the assumption turns out to be wrong.
So the short answer is this: the quality of your documentation largely determines the quality of the pricing you get back. Well-resolved construction documentation lets several builders price the same scope in the same way, which is the most reliable way to compare their numbers fairly. Thin documentation produces quotes that look different because the builders are pricing different jobs — not because one builder is cheaper.
That matters most on higher-end work. A large renovation, a second storey, or a custom home has more junctions, more finishes and more coordination between trades than a standard project — which means more places for an assumption to hide.
A builder pricing a job is really doing a take-off: counting, measuring and specifying every item that will end up on site. What they need to do that accurately:
| What is missing | What the builder usually does | What it costs you |
|---|---|---|
| Construction details at junctions | Prices a generic solution or excludes it | Variation when the real detail is resolved on site |
| Finishes specification | Inserts a provisional sum or allowance | A number that is not a real price, and moves later |
| Structural coordination | Adds contingency, or raises an RFI | Padded price, or delay while it is answered |
| Existing conditions on a renovation | Prices cautiously and excludes the unknown | The riskiest part of the job stays your risk |
| Window and door schedule | Assumes standard sizes | Rework or re-order when the real sizes arrive |
None of this is a criticism of builders. Contingency and exclusions are the correct professional response to an incomplete drawing set. The way to get a tighter price is to remove the reason for them.
A variation is usually not a builder changing their mind. It is a gap in the documentation being discovered at the worst possible time — after the price was agreed and after the work has started.
The sequence is fairly predictable:
Every stage of that sequence traces back to step one. Detailed documentation does not make variations impossible — client changes and genuine site discoveries will always exist — but it removes the largest and most avoidable category of them.
RFIs work the same way. A request for information is a builder asking a question the drawings did not answer. Each RFI is time, and on a busy site, time is cost.
There is a common assumption that a high-end project can be worked out as it goes, because the budget has room in it. In practice the opposite is true.
Budget drift on higher-end projects is rarely one big mistake. It is a long series of small undocumented decisions, each resolved on site at whatever the answer happens to cost that day.
Both, but the documentation benefit is the more valuable one.
Design Science models every project in 3D in Revit before it is documented. The practical effect is coordination: the model is a single source that the plans, elevations, sections and schedules are all drawn from, so a change in one place updates the others rather than leaving a contradiction behind. Clashes between structure, services and architecture surface on screen instead of on site.
It also makes quantities more reliable. When a project is modelled properly, it can be measured properly — which is why a considered bill of quantities is possible at all.
The 3D visuals clients enjoy are a by-product. The reason for modelling is buildability.
This is the hardest case for accurate pricing, because the biggest unknowns are inside an existing building.
Measured survey and 3D scanning help here. Capturing the existing structure accurately — real levels, real wall positions, real out-of-square — means the new work is designed against reality rather than against an assumption, and the builder is pricing against the same reality. Design Science offers this through its scanning and as-constructed documentation service, and it is most useful on older homes, unusual geometry, and any project where the new work has to meet the old work precisely.
It does not remove every unknown. What is inside a wall cavity or under a slab still has to be opened up. But it narrows the unknown to the things that genuinely cannot be seen.
Detailed documentation costs more to produce than a minimal set. The question is whether it costs more overall, and on most higher-end projects it does not — because the money saved sits in the construction number, which is the far larger figure.
There is a second point that matters just as much. Documentation is only useful if the thing being documented is buildable and budget-aware in the first place. A drawing set that resolves every detail of a design nobody can afford is a very thorough way to waste money.
This is where David Steadman’s dual background is the practical difference. He holds both a QBCC Builder’s Licence and a QBCC Building Designer’s Licence — fewer than 1% of practitioners nationally hold both — and has over 30 years across the trades, estimating, project management and building. The design decisions are made by someone who has priced and built the outcome, so buildability and cost are considered while the design is still on screen, not discovered later on site.
Design fees at Design Science typically range from 4-7% of construction cost, starting from $3,000 for smaller projects. That is a wider band than a minimal drawing service charges, and it is deliberate. What sits inside it is the work described above:
The percentage moves within that band according to the complexity of the project, not the size of the drawing set. A straightforward extension sits at the lower end; a bespoke custom home with significant structural and services coordination sits higher.
The comparison worth making is not fee against fee. It is fee against what the documentation removes from the construction number, which is the far bigger figure and the one that determines what the project actually costs you.
A short readiness check before you hand a set to builders:
If the answer to the last one is no, the quotes you get back will not be comparable.
Detailed enough that the builder does not have to guess. In practice that means a coordinated construction set with details, schedules and a specification — not just a planning or approval-level drawing.
Usually not. Drawings prepared for the approval process answer the assessing authority’s questions. They are rarely detailed enough to build or price from, which is why construction documentation is a separate stage.
No. Whether a price is fixed, and what it excludes, is a matter between you and your builder under your building contract. Better documentation improves how accurate and comparable the prices are — it does not by itself change the contract type or remove the builder’s right to price risk.
No. Client changes and genuine site discoveries still occur. It reduces the avoidable category — variations caused by the documents not answering a question.
No. Approvals are decided by the relevant assessing authority and, for building work, a licensed building certifier. Design Science does not issue approvals and does not act as the council or the certifier. It prepares the design and documentation, and can coordinate with the relevant consultants or approval professionals as part of a broader design project.
That is the main reason to invest in them. A single well-resolved set sent to several builders is the most reliable way to see who is genuinely more competitive, rather than who has assumed less.
If you are planning a renovation, extension or new home on the Gold Coast and want the documentation right before you approach builders, the first step is an initial consultation.
It is a paid professional assessment rather than a sales meeting. The consultation fee is $280, and it is credited in full against your design fee if you proceed.
David Steadman
Licensed Builder & Building Designer
David Steadman is the founder of Design Science, a Gold Coast building design practice backed by over 30 years of hands-on construction experience. One of few Australians holding both a QBCC Builder's Licence and Building Designer licence, David brings a rare combination of design thinking and practical building knowledge to every project.
Fully insured • Personalised consultation • Transparent pricing
Transparent pricing with no hidden costs. Every project includes full 3D digital modelling, detailed construction documentation, and a complete bill of quantities.
Request a Consultation