You may want to post this is the studio forum.
That being said, it depends on what you want. A live drum room, requires something different than a vocal tracking room, vs. guitars tracking etc. If possible you want to avoid a square room.
If you're main goal is to have a room that you get get good drum sounds in, you likely would want a larger area with wood floors and walls. While it is possible to also get good vocals, you may need to set up a corner with specific treatment for vocals.
I have always thought my ideal "music room" would be about 40' x 40' with wood floors and walls. A small 5' x 5' vocal booth in one corner. A small recording box in another corner (to put guitar cabs in). Naturally, the room would not be square, but rather have some angled walls, with various treatment. Unfortunately, I've never been able to make much more than a 20' x 20' area available.
