I've made a mouse skyscraper using a 4ft glass tank. Made a frame and doors using sheet wire mesh, and fitted shelves using strips of wood and cat litter trays. Originally used PVC pipes surrounded in twine to let the mice run between levels, but the wee bu**ers kept hiding in them every time I came to take them out, so now have a ladder system and suspended wooden branches. I have 8 mice in there at the moment, but the tank could easily take 16+.
With the shelves in:
Fully furnished for mice:
With new branches and ladders between levels:
Side view:
Bottom two tiers:
Top two tiers:
Of course they're always running up and down the mesh! You can get the 6mm mesh from Homebase in sheets. I used HA6 silicon sealant to hold everything to the glass.