Bad advice from above. You want to develop, build then sell.
With a granny flat you never get 100% of the cost back.
I.E. Spend $500k on block, spend $90k on granny flat. Unless there are direct comparables you would be lucky to get $600,000.
Factory in holding costs and outgoings/agent fees you will lose.
If you want to develop you need to begin with a duplex. You can save costs by being on site and managing the project, easy and straight forward process. You can sell and make circa 10% after one year, 20% if you are good developer.
