My toy is 48x105x14. Its a Morton building. I have a 12x12 door in the front on the 48 side. It is fully finish on the inside with 6 inches insulation in the walls and 24" in the ceiling. I have heat in the floor and also a trench drain running 60' in the center, with the pitch of the floor at about 1/4 per foot. The floor with drain completely without any squigging.(Spelling)
It holds my 38 footer, the race car, two show cars the gator and two John deere tractors. I still have plenty of room to hold all my other toys from home. I might suggest that you look at garage journal.com this is a site about building toy boxes such as you want. There is all kind of guys building pole garages and other ones for their toys. I spend as much time there as I as do here on OSO.