This new updated version of my corner guinea pig shelter as got 2 off  5"×5". Entrances the size is 12"×12" x6" high.

Its got no bottom which makes it easy to clean, just keep moving it around.(Its not painted but most people have some spare paint left over in their shed or garage which would be suitable.) As these are made from plywood there may be some cosmetic marks on the ply but this doesn't affect the item