1. The guest house.
Regular, ordinary Americans do not have one of these. We're not all that rich.
Some homes (quite a few, actually) have the room where you park your car(s), built right into the structure of the house. That's called an attached garage.
2.The detached garage.
The separate building that sits to the side or slighty behind your home is called a detached garage. Sometimes there is an apartment located on the upper level of the garage that's just like any other apartment: living quarters, plus bathroom facilities.
Some very lucky children have a tree house in the backyard. I'm sure you're not talking about this kind, though.