When one of my friends had this kind of opportunity, she and her husband structured the attic of the garage so that they could build rooms up there. She got the back half (with the great view) and he got the front half....his entrance was through the garage, hers was off the kitchen....there is a door between the two sections that is usually left open, but it gives them each their own space. When they first built it, they didn't have much money so they just added the right trusses and beams, then added on and finished it as they had the money....it has worked out really wonderfully for both of them. Have fun.