What kind of contract you're signing. Group home builders use one of: NZS 3902 (the standard residential building contract), a Master Build–branded variant, a Certified Builders–branded variant, or their own bespoke document. The first three are well-understood. The fourth is a flag to take to a lawyer.
Fixed price vs cost-plus. Fixed price means the contract sum is the contract sum, save for variations and PC sums. Cost-plus means you pay actual costs plus a margin — usually higher trust required, usually higher cost in practice. For a first home in a group-home setting, fixed price is the default and the right choice.
Provisional sums (PC sums). These are line items the builder has costed as a placeholder. Tiles, light fittings, kitchen appliances, sometimes flooring. The amount is in the contract; the actual cost is not. If the PC sum is $8,000 for tiles and you spec tiles that come to $14,000, you pay the difference. Make sure every PC sum is realistic for the spec you actually want.
Variations. Any change you (or the council, or the engineer) ask for after signing. Each variation should be priced and signed before the work proceeds. If your builder is doing variations on a handshake, document them yourself in writing the same day.
Progress payments. Most contracts trigger payment at defined milestones — deposit, foundation, roof on, lock-up, practical completion. Match the payment schedule against the build sequence above; don't pay for stages that haven't started.
Liquidated damages. If the build runs late beyond the agreed completion date, who pays whom and how much? Many group-home contracts are one-sided here; the late-completion penalty on the builder may be capped low or not present at all. Worth understanding before you sign rather than after.
Final tip: a residential build lawyer will read the contract for an hour or two of their time and flag the things that matter. The cost is small relative to the build cost. Spend it.