1. Use Experts who do this as the main source of income for their company.
2. Look out for the cheap granny flat builds, as it might cost you a lot more in weeks, months or years to come.
3. Check that the area is suitable for a granny flat. Are their potential tenants interested in living granny flats in this area?
4. Research the granny flat market in the area. How many are available for rent? What are the agents saying: easy or hard to rent?
5. Assess the potential resale value with and without the granny flat?
6. Do the numbers with your accountant.