The first step before you even pick up a nail or lift a hammer is to undertake a site assessment of your block. Ensure that the property information for your block such as vegetation/tree removal controls, planning overlays, service connections, bushfire attack level (BAL), termite risk, and flooding levels are all assessed by your builder.
Your builder should also engage a licensed surveyor to assess the site fall, including proximity of adjacent properties and trees. Your builder should also engage a professional soil engineer to provide a soil test that will determine the type of slab or footings system for your new residence.
This information will help to determine the site costs for your new property up front. Site costs can include things such as footings design, site cut and/or fill, whether retaining walls and agricultural drainage are required, and site protection works for adjacent properties. Rock excavation and removal can be difficult to assess, and is usually an estimate based on the soil test (which can be included as a provisional sum amount in the building contract).
If your block is titled, all of this information should be available for your builder to assess, who will then appoint a structural engineer to design the footings/slab for your new home. This will enable the site costs for your new residence to be fixed well before your final building contract price is determined.