Many families do not fee comfortable with a bedroom down in the basement. Another option you may wish to consider is a home office. Being in the basement allows for fewer distractions, and a properly wired home office is a more affordable but desired option for many buyers. If you still wish to have it as a 4th bedroom, you may wish to do it as a home office, build a closet, and allow the realtor to list it as a guest room/office, staging it as an office but showing the bedroom potential with a day bed/chaise sleeper. A man cave is least likely to draw buyers attention.