New Dedicated Audio Room

I am in the initial stages of buying and building a new home. This home is going to have a dedicated audio room. (Approx 18'x 26') I will be working with the builders regarding the room and want to hear some suggestions regarding sonic improvements. I plan on using Hubbell outlets with 4 dedicated AC lines. I am also going to have the builders use thicker sheet rock for the walls and ceilings. Any other suggestions??
Ideally if you can keep any of the parallel walls from being absolutely parallel, that is a plus. Minimizes standing waves. A cathedral ceiling is a plus also. Sounds like a nice room to start with. I would also talk with a room acoustic expert for professional advice since you are going through all the effort you are, it will be worth it in the long run. Good luck has sheet rock replacements that are sonically absorbative. I'd call them.
Be careful about getting too absorbative. I don't think you want a room that is too absorbative. You might end up with an anecholic chamber sound that will improve one thing (imaging) at the expense of the music coming alive. It is however a matter of taste. I personally don't like that dead sound. It doesn't sound like the real thing to me. Check with a professional first.
I built a dedicated listening room in my old house and if you want, I would be glad to send the plans and description of the room my contractor built. Give me a name and a FAX number and I will send it. It turned out excellent. Was very musical, dedicated lines, and sound proof.