Were they in NSW? Isnt the legal limit 60m2? Who was your builder? What happens if the tenants get injured in your extra shed to make it 90m2? Does your insurance cover it?
It's all legal and covered. They don't live in it. Part of sepp you can attach ancillery structures to a granny flat. Shed, awning, patio etc. It is only the habbitable area that has to be max 60m2. I was just giving you examples of granny flats i have built and what they cost.