Contracts for work over $30,000

Contractors must provide a written contract for residential building work costing $30,000 or more (including GST), when working directly for the homeowner.

It's your responsibility to provide a written contract to your client. There are certain things your contract must cover, including the payment process and schedule, and how disputes would be resolved.
If you don't have a written contract or if the contract doesn't include the minimum content specified in the regulations, there are default clauses that are automatically considered to be part of your contract. You can be fined $500 for not having a written contract if it is required.

If you are a subcontractor reporting to a main contractor, these requirements don't apply to you, regardless of the value of your work.