I am looking for any ideas on how difficult and how much it would cost to have a bonus room added on top of my existing garage. I have a small 2 story colonial with a large 1.5 car side load attached garage. The garage footprint is roughly 20'x20'. The current garage is all exposed framing and has no finished attic space or insulation. The only side that has drywall is the side that attaches to the house. The house is built on a crawlspace and the existing block foundation wall was extended around the garage and a concrete floor was poured. As a result, I do not believe there would be any issues with the foundation being able to support the load of a second story.
The main question I have is how much would I expect it to cost to rip the existing roof off and add a second story? Our basic concept for the second story would consist of a large dormer window facing the street side of the house with a sloped roof line that squares off after the peak as it goes to the back of the house. The back side of the addition would probably be cantilevered ~2' over the garage to match the rest of the house and maximize the added space.
Electric would need to be fed in from the garage below, the ceiling of the garage would need to be insulated and vented, a doorway added to the bonus room from the top of our existing 2nd floor stairs, and ductwork would need to be extended to provide a couple of additional vents to the room (assuming existing heat pump is adequately sized for the additional space). If anyone has a rough idea on what I could expect to pay to add a bonus room of this scale, please respond to this thread. Any help, input, or recommendations would be appreciated.