GARAGE LITTERBOX FOR INDOOR CATS: We did this when we moved in our home. Installed a cat flap door to the garage. Placed litter box in a thrift store dog cage (so kitty would not wander around a garage of chemicals and tools or run out when the garage door opened). She learned to use it immediately.
Our version of a garage litter enclosure, thanks to the ideas I found right here on Pinterest! The cats enter from a cat door in the entryway. It's quite a success! Look for other versions right here on my Pet board.