I'm wondering what spec motors it would take to build a Roomba-like cat ride?
Cats riding Roombas is pretty common.
Make sure you add a couple of joysticks, then, so your cat can control the direction and speed. Please post some videos on youtube when you get done.
Depends on your electronics skill-set. If you find a roomba "for parts" doing something called the circle dance, you can fix it if you can solder and are goid at taking stuff apart and getting it back together. Hard to beat a pre-made robot chassis.
Are you going to add an insanity mode like in Tesla cars?! [ If so make sure the top is designed for good claw traction ]