My Scout is about 6' 2" tall and around 6'+ wide. Originally the bus was around 6' tall in the center and considerably lower towards the sides. My Scout isn't rounded like the bus roof so fitting inside was going to be a problem. I'm 6' 2" so I couldn't even stand up in the center. Since the front wheels of the Scout park on top of the rear wheel wells of the bus that raises the front of it another 9". I do know of Jeeps fitting inside a bus but they are shorter and probably narrower. As you can see by the following picture it sits pretty tall in the bus compared to the original roof.
(click to see larger version)
Even smaller tires weren't going to get it to fit under the roof. I believe we raised the roof to 7' to give enough room. The walls and roof were reconstructed out of 1"x2" steel. The 1x2's were bolted inside the existing wall/roof supports. We purchased a lot of steel and I was glad we did it before the jump in steel prices. The outside of the bus was initially covered in 1/4" plywood for rigidity and then that was covered using 24"x50' rolls of prepainted aluminum trim coil (thin stuff) from the local home improvement store. It's held on with contact adhesive (no ugly rivets or screws showing). I'm not sure how well this is going to work in the long run so I'll have to wait and see.
Right now I have no plans for a bathroom. I know how I could probably fit one but I'd loose access to the back. Eventually I may decide to do it.
Just remember, building a new roof is no easy task (not to mention finishing the inside). Once is enough for me.