One of the first things you should arrange prior to designing the buildings on the block is a contour survey of the land, a contour survey provides information on the elevation of the land and also situations of sewerage, water and power connections as well as positions of existing fences and trees.
Generally, a builder will arrange for a contour survey prior to providing a building design, I found the most benefit of arranging the contour survey myself was the home builders took me more serious, after all a contour survey is a one-thousand dollar investment.
I arranged my contour survey with Cottage Engineering, a Perth based surveyor company. It cost me $975 which also included $180 for Australian Height Datum (AHD). AHD is an elevation standard which assumes a zero metre elevation is at the average mean sea level. One of the builders informed me it wasn’t really necessary and only needed if the land is situated near the ocean.
Cottage Engineering even provided the AutoSketch SKF file, which was handy for the builders.