i thought about these things quite a lot before... i always come down to having one large general-purpose type of room and a few specialized ones like bathroom or kitchen.
whether or not id like to have my bed in that room i dont know... id certainly like it to be close to it, but not necessarily directly in the room. maybe having an appropriately-sized niche in the room that can be closed with a curtain if necessary. nah, on second thought, i love watching tv from my bed way too much. no way the bed could be out of that room.
(two tvs isnt really an option, as the tv is inevitably linked to video game consoles, and having them double... would be expensive and id need to walk back and forth to get the games i want to play to where i want to play them)
other than that: lots of bookshelves. a corner of comfortable sofas with a small table, facing tv and stereo. separate table with computer and surface for reading/drawing.
style wise, id opt for white walls and dark, almost black parquet floor. <3
practically speaking, a sofa/bed combo would probably be very practical. on the other hand, i pretty much use my bed as sofa right now and its pretty great, so i could just continue that tradition as its kinda cool. a larger bed than i have now (standard size) would be comfortable.
i still ponder whether to have fitness equipment in the room or not. i guess rather not (but close nearby, definitely in range of the stereo) because weights will damage the expensive parquet (falling barbell O_o), movement around a heavy bag would be quite suboptimal and its not the best surface to skip rope on either. thats quite sad because i think a solid black leather heavy bag makes nice decoration.
but i still guess that this is left for a close-nearby room: slightly padded floor, heavy bag (black, leather, long enough for lowkicks), a power rack, bench and barbell (plus two dumbbells), space enough to allow for movement around the bag or skip rope.
the main room, however, should be sleek and simple in design, furniture matching. id love to have an own room for keeping clothes instead of a wardrobe.