Hi dynamite,
1. Locality map indicating location of subject property
2. Site survey or mud map showing all major features (street, fall, trees, house, hard surfaces, garages, north, views, easements, rights of way, etc.) if survey is not available
3. Plans if available or again sketch plans showing plumbing and load bearing walls etc.
4. Lots of photos internal and external from all directions
5. Your budget
6. Your time-frame and time-line
7. Your ideas (sketches) on paper
8. Council zoning for area and block
9. photos of any developments similar to the one you have in mind
10. Photos of developments in the area close to the proposed
Most of the plans, surveys should be available from the owner via agent or from council (with owners consent), otherwise it's up to your drawing and interpretation skills. All part of your 'rough due diligence'
regards, MC