Working with a building designer: from rough idea to approved drawings

What a building designer actually does

The work runs in stages. First comes a site measure and concept design — turning your brief into a floor plan and form that works on your block. Then developed drawings, where materials, dimensions and compliance details firm up. Finally, full working documentation: the drawings your builder prices from, your engineer coordinates with, and your council or private certifier approves against.

Designers also commonly coordinate the supporting cast — structural engineering, energy assessments, surveys — and can manage the approval submission itself. That coordination is genuinely valuable: consultant reports that don't talk to each other are a classic source of delay.

When would you use an architect instead? For highly bespoke design ambitions or complex sites, architectural fees can earn their keep. A draftsperson, at the other end, suits simple documentation of something already fully decided. The building designer occupies the wide middle.

How the fees work

Fees are staged to match the work: concept-only engagements sit in the low thousands, full documentation for an extension runs to five figures' edge, and complete new-home design with consultant coordination goes beyond that. Some designers quote fixed fees per stage, others a percentage of expected build cost — a few per cent is the common shape. Indicative only, and heavily dependent on project complexity.

The stage structure protects you: you can stop after concept if the design isn't working or the budget maths isn't, having spent a fraction of the full fee. What costs extra almost everywhere: major design changes after you've signed off a stage. Decide slowly at each gate; redrawing is dearer than thinking.

Choosing the right designer

Building designers are registered or accredited in some states and not others, so check what applies where you live — and ask about professional indemnity insurance either way. Then look at their actual output: ask to see a full documentation set from a past project, not just pretty renders. You're looking for dense, specific drawings — dimensions, sections, details — because vague drawings become expensive builder variations on site.

Fit matters too. A good designer asks about how you live, your budget ceiling and your appetite for approval risk before drawing anything. One who sketches your extension in the first meeting without asking what you can spend is designing for their portfolio, not your project.

Mistakes to avoid

Design-stage mistakes are the cheapest to make and the most expensive to keep. Almost all of them are scope clarity problems.

• Not asking exactly which drawings, consultants and approvals each fee stage includes
• Signing off concept drawings you don't fully understand — ask for a walkthrough of every room
• Designing without a build budget, then discovering the scheme prices at double your ceiling
• Skipping the engineering and energy coordination, leaving gaps between consultants
• Making big changes after documentation has started and expecting them to be free
• Choosing on fee alone — thin documentation costs far more in variations than it saves in fees