IKEA STUVA litterbox for 4 kitties - mine would probably prefer two separate chambers. The trofasts have very low sides, though -- you'd want to use high-walled boxes so they didn't kick litter everywhere. Then you could put standard cabinetry on top.
Litter box cover from 2 IKEA side tables and fabric! This is a great DIY for cats, better than traditional covered boxes because it doesnt have plastic on the sides, which can trap odors and make some cats reluctant to use the box as often as they should.
Kitties are cute, but kitty litter boxes are UGLY! This tutorial shows how to make a DIY kitty litter cabinet that hides a litter box and has extra storage for litter. Plus its attractive enough to display in a kitchen or dining room!