My roommates cat stinks... I can't figure out why.?

he needs to try feeding his cat Felidae dry food, if cat's stool still smells bad try to give him digestive supplements. Buy a flushable litter and dispose of the poop right when you see it, not having to use plastic bags makes it much easier. You can also buy one of those deodorizers which spray automatically every 9-30 minutes, it will help to cover-up the smell.