An alternative would be a prefabricated home that is basically made in a factory and transported to your site. They're fully finished, you just need to put furniture in them. They can be completed in around 12 weeks so you basically save on building costs and all the headaches of arranging tradies. BUT, they're not cheap - the ones we were looking at were quoting $2K per square metre.

We're now looking at converting a shed (9m x 6m) into a granny flat. They can look quite funky if you do them properly and from preliminary research, I think they can be done for about $1K per square metre. Building seems to be quite simply. We'd be relocating our existing shed so we just need to get a new slab poured, move the shed and get it insulated/lined by a builder/chippie and ditto internal walls.