The best way to strive for no variations on a project is to spend the time Up front understanding the project desired outcome and engaging the Contractor to a reduced design responsibility from Construction Certificate including all fees to a defined Practical completion milestone. This can be achieved by including in the tender with the following items for a green field site; Design and Construct contract like AS4902 where the definition of Practical Completion includes approved As built documentation and Occupation Certificate.
DA approved certificate including all drawings obtained by a Third party, A Geotechnical report, Service connection details Detailed Principal requirements brief.
This provides and defined start to end milestone with no third party involvement not contracted to the Builder and off course the Client can’t make any changes.