I just have like my really favorite ones, right now only my WRX STi and my Hummer out. I just go and buy those really cheap plastic cases from Wal-Mart and they work out great. The others, I just have under my bed. I use them because you can just move one of them. When I grow up though and have my own house, I'm going to make a room just for my cars.
I shall car it... a GARAGE!!!
Just kidding, I'll have a room in my house for my model cars.