Back in 2014, I featured an alternative litter box idea: I proposed this stainless steel steam table pan to be used as a kitty toilet. Since then, several cat supply brands have picked up on this idea, and there are many more choices when shopping for a stainless steel litter box for cats. You can see some alternatives below.
Stainless steel seems like a no-brainer material for a cat litter box -- it's stainless! Metal boxes like this one with smooth corners and straight sides are easy to clean and this type of material won't retain odors or stains.
The box featured here (the exact same one featured all those years ago) is very close in dimensions to a large standard litter pan you'd find at any pet store. The box measures 20.9" by 12.9" by 6.1". The pan has a small outer lip that is curled under at the edge, so it's safe for your cat to enter and exit. The strong box is also surprisingly lightweight, making it easy to work with and clean.