Rives has proved to me to be extremely knowledgeable and has devoted a great deal of time to this site helping people like yourself. I would look at his site as a start and consider using his services. You have a good size space to start with, the biggest issue I expect you'll confront is the height. Given a basement room, I expect the height is plus or minus 8 feet. This means the "perfect size room is 15.2' x 11.2'. The largest "preferred" size with 8' ceilings would be 17.6' x 12'. Given this information, Rives my prove to be even more valuable than first thought. The good news is you will more than likely have extra space where you could create a base trap and an equipment room. The other good news is you will not be short on size, so given the right design you should be able to create a great listening environment.
Now if you want to go a little further, one thing I've done for clients in your situation is to excavate the basement floor down a few steps. A ten foot ceiling would give you a 19' x 14' or 21' x 15' room, still leaving ample room for steps and a base trap.
Now if you want to go a little further, one thing I've done for clients in your situation is to excavate the basement floor down a few steps. A ten foot ceiling would give you a 19' x 14' or 21' x 15' room, still leaving ample room for steps and a base trap.