… create a garage if you have no immediate need for a forth bedroom, but ensure it’s built in a manner that would allow you to easily convert it into a bedroom, if needed. If the garage has a window, plug sockets, etc, it’s just a case of bricking up the entrance, plastering, and you’re pretty much done. You could turn the garage into a bedroom within a week.

— Do. - Garage or no garage (some sound advice)