Personally I would do it. I never used or even wanted a bonus room before and do you need a closet their. It's like having a closet in your family room. What is the idea of the fin. Dormer? I would personally attach the fin dormer to the side of bed 2 and add more living space and maybe even a bar set up in that corner as well as extending the master closet. Lose space on one side but add to the othe side while taking surface area maybe some costs of construction too.