I converted our double garage into a playroom and it does work to a large degree but they do still bring toys into the house. They also still have toys in their rooms so there are often toys somewhere between the lounge and their bedrooms. But it is only a handful of toys - not a whole box of duplo or anything like that.

I got some cheap clearance lino to put down on the floor and some clearance backed fabric from spotlight to hang across the garage door to keep the heat out. I also had an air conditioner put in but we live in NQ so we wouldn't be able to use it six months a year without the air conditioning.

Because it is just the garage, we installed brackets and planks of wood as shelving - we didn't need to worry about expensive shelving. It's all sanded so no splinters but we didn't even paint it. We also have an old lounge suite out there so I can sit out there while they play and when we have visitors with kids, we sit out there too. I have my playroom set up in areas ... actually, I blogged about it not long ago ... Adventures in the Ville: Our playroom