I have a 15 on a 22 ft wide garage, Tried for years to call it a 2 car and 2 would fit but barely. I would heavily consider the aesthetics of the building. I'm in MA and traditional style around here seems to favor the 2 smaller doors. Also, if you have a pretty wide building, 2 separate doors may help in getting vehicles in there with some working space around them. And like someone mentioned, a super wide header presents structural considerations to deal with. Not saying it can't be done right, it just may be kinda spendy.