+1.
No expertise required. You can't do it unless the block is 900sqm.
You have 2 options
- granny flat
- MAYBE a single dwelling if council agrees. This is a single bedroom dwelling, no more than 70sqm on it's own title and the amount of land required varies from council to council - sometimes half a lot, sometimes 2/3rds of a lot. So generally you'd need 300sqm for this but sometimes as low as 225sqm which would work for your block.