If you are looking to achieve good sound, I would begin by constructing the room to the proper proportions of length, width and height. Search out an acoustics book, such as the one from F. Alton Everest for information on the "golden rule" proportions. More than anything else, this can make a huge difference. If you are unable to construct to these precise proportions, a declension of choices is offered. Then, to reinforce bass, I would build on 16" stud centers drywalled using two layers of 5/8" plasterboard. Avoid the tendency to insulate using expanding foam, as this will make the wall resonant. Also, avoid building on 12" stud centers since (in my experience) this is less optimal than 16". And, as long as you are building the room, be sure to pull through a couple of dedicated 20-amp lines for power (hanging your valuable equipment on a weak 15-amp circuit wired with 14-2 is something which can't be cured by an expensive power cord). Finally, once the room is finished, carpet in wool vs. nylon, which contributes to "ringing". Then, pull out a test disk (such as Stereophile Test Disk 3) and a Radio Shack sound pressure meter to see what issues remain. These can be treated through judicious use of acoustic treatments (at side wall, front wall, etc. reflection points). Select the treatments based on the frequencies that are causing the problems. Before treating the room, take special care in placing speakers and furniture. And locate the front-end equipment where it will be less prone to structure- and air-borne vibrations. After all, the purpose of building this type of room is to optimize all variables. And, there is no substitute for placing equipment where it wants to be vs. where it needs to be to coexist with other things (in a non-dedicated room). Just my two cents. Good luck! It's kind of like a laboratory experiment. It will take a little time to get things right.
Joe.
Joe.