Few city lots have enough room to add onto a home at ground level, so most homeowners opt to go up. Another solution would be turning the garage into living space, but then you wouldn’t have a garage!
We have had many requests to build a partial second floor for our Whatcom County clients, and they have been happy with the results. Usually this involves constructing rooms over the garage, and for the average 2 car garage, this will give you a 500 square foot space, which would provide a nice sized master bedroom and bath with walk-in closet.
Don’t forget the need for stairs for access; these often are built into the garage.