Finally found a jumbo box that's made for my cat. Other covered boxes were too cramped, so I had to remove the tops and just use the pans. My cat is not fat, just bigger than average. She's 9 years old, has long hair, and blind in one eye. Because of this, she inevitably missed the mark and sometimes urinated over the side of the litterbox. She also buries her waste with tremendous enthusiasm and I had litter all over the place. 
This box solved these problems. It's big enough (with cover) for her to use comfortably, and I don't have to vacuum everyday. Great box for bigger, and or bulldozer kitties!