My cats have a litterbox room. It's like an extra large water heater closet in the garage that they can access through a pet door in the laundry room. I have 6 boxes in there for them. The people we bought the house from made the room for their three cats. It was great for keeping my dog Disney out of the boxes since she thought they were the snack bar.

I also keep one in the garage for Ripley. He likes his "alone" time out there.