I saw this homemade car garage for toy cars over at What do we do all day? and made it for some insta-fun. I used a Pop-tarts box. I cut off one side and use it (and lots of tape) to make the central level.
We also used an empty animal crackers box as a makeshift airplane hanger.
I made this for Dalton, and even though he's in none of the pictures, he enjoyed playing with it, too.