What are your expectations and budget? A converted school bus will get you there, but it's going to be a bare bones chassis that will ride and handle like that, it will be noisy because the motor is at your feet. They're built with simplicity and safety in mind, a cheap way to get a bus load of kids to school.
I've got a 93 Beaver, it has a welded aluminum frame for the house and a Gillig chassis. Country Coach, American Eagle, Monaco, Holiday Rambler (and others) also built similar motor homes. The quality is amazing, even being nearly 30 years old the ride is smooth, it steers and handles well with no after market band aids. 3/4" face frame walnut cabinets that are screwed together, I've disassembled several and not found a single staple, every door and drawer works like new. The roof is one piece of molded fiberglass, low maintenance and not a lot of chance of leak if you keep up with the sealer on the vents, antenna, skylight and drip rails.
More than anything it depends on how you expect to use the RV. Short local trips the school bus would work. Otherwise I'd look for an older high end motor home.