Thanks to Angrysquirrel for uploading their quite realistic looking school bus model. My daughter asked me to print a school bus for her dolls and nothing else quite fit the bill. I enlarged it, hollowed it out, and divided it into printable pieces.

*Edit: I added an option to print without bearings so you can resize as you wish with the new “NoBearings” wheels, axle, and axle fastener STLs. The axle fastener is to go around the axle and attach to the main body. I'm not sure how well it will roll with this setup. Or, If you're not concerned with rolling, you could just glue the axle directly to the main body. 

The print in the pictures is printed at 125% size of the files that I uploaded. You will need 4x 8x22x7 “skateboard” bearings for the wheels. *Since there are bearings involved, the axles and wheels are not easily scalable but I have included the axle and wheels for the 125% size.

There will be glue involved. Lots of glue. I recommend starting with the 2 “floor” pieces on a flat surface and building around that, finishing off with the axle and wheels. Be sure not to glue the roof pieces onto the main body so there is access to the inside.

There are 2 options for the front. The first will require a lot of supports and is what I used in the pictures. The second option is what I made when I started actually using my brain (that's still debatable). It uses much less supports and only requires 1 more piece to glue on. You will still need supports for the fender, wheel well and windows.

I included a “BottomReinforcement” piece which is just a triangular prism. After everything else is assembled, this is meant to be glued on the bottom of the floors to reinforce the seams where the two floor pieces meet and the middle floor meets the front to help alleviate downward pressure during use. I used two per seam on mine. Use as many as you deem necessary.

I know this isn't the most elegant assembly process but my kids sure seem to like playing with it and I hope yours do to.