We've been looking into garage apts as well .... still haven't made the decision though. 1) Not sure. The space can't be counted towards your house sqft because it is detached. So you are lucky to get your initial investment back bt not more than that 2) Call a couple of builders 3) We had Harvard Heights come by but they weren't very responsive to our request. Rod Frego quoted $80k finished for a 22' x 30' garage + apt. All Star construction quoted $80k for shell and $100k finished 4) see 3)