Sorry, I posted this in the garages forum but figured this may be a better place.

I am currently renovating/rebuilding a 1,500 SF two-story home in Honolulu, Hawaii and I'm debating if I should convert half of the two-car garage into a fourth bedroom.
I am mid-construction in a heavy gut-and-rebuild renovation project. The contractor is a close friend of mine so he doesn't mind if we make changes midstream as long as it's not undoing what was already completed. They just poured the slab and I'm having second thoughts on the garage space. When I purchased the home, there was no garage whatsoever - just parking in front of the house. So I completely redesigned the space and added a 20 x 20' two-car garage which is attached to the home. There is a 24' long driveway between the street-side property line and the front of the garage door so plenty of room to fit two cars comfortably off the street and in the driveway... but of course the cars will be exposed to the elements. However, in Hawaii that is just sun and occasional rain. We never worry about snow or freezing temperatures. You sometimes have to walk into a fairly hot car and get rained on a little (So I'm thinking of taking the 20 x 20' space and converting the back half into a fourth smaller guest bedroom with a nice sized walk-in closet. It will give me about 180 SF of usable space. The space would not look like a garage at all because the garage door, motor and tracks will be in the front half of the garage behind the new wall. From inside the house, nobody would ever know there was a garage intended to be there. I'm basically drawing a line halfway between the front of the garage and back parallel to the garage door and building a 2 x 6" wall with 5/8" drywall and lots of insulation. I am installing one large 6' x 4' window which will actually provide a little bit of cross ventilation as long as the bedroom door was open. I should note that there is street parking available so if guests come over there is a place to park albeit less convenient.

The benefits are that I will have a fourth bedroom which should help me on the appraisal value more than having a garage alone. Also, I would only assume that I could maybe get a little more rent with that fourth bedroom because I am still maintaining two parking stalls with the new extra long driveway. From the outside, the home will look very conventional with a driveway and two-car garage door with main entry to its side. I was told by friends I should get rid of the garage all together and convert to living space but I think keeping that two-car garage door visually helps the curb appeal even if when you open it you can't fit a car in it. If I convert half the garage, the new garage will only be 9 feet deep by 19' wide. A very nice-sized and easily accessible storage space or workshop but definitely nowhere near enough to park even a tiny car. The only car that may fit would be a Smart car. Is this a crazy stupid idea or does it actually make sense?