I could barely afford to build a garage let alone a structure that is a pseudo house.
How about something like this? All you need is a set of bigger doors (possibly a little height on the second floor) and you would be in business.
This barn structure is located on Route 66 just outside of Yukon, Oklahoma picture was taken 3-7-2011
That is really nice looking building, but my big fear would be if you got a fire anywhere in there, you lose the bus and the house all in one. I could stand losing the bus or the house but not all at once. Yea if it's in a barn next to the house and a tornado comes by I may lose both. I know you can't eliminate all risk, but I do try to minimize when possible.