The kitty apartment is a great concept. I attached another cage of this manufacturer to the lower door, for the litter box, allowing more space. I used my cage for my sick cat and it was incredibly helpful. The soft cushion and movable shelves are cat friendly and allow for various perch heights and exercise potential. Not so great are the wheels that don't function well; great idea, but the wheels don't turn together and are flimsy.  My biggest concern is the lack of structural safeguard to ensure that the cage does not collapse when set up. There should be a way to lock in the roof section and sides.  Overall, this is a great cage designed to meet the needs of kitties.