Home Theater Advice
Room Construction
1. Make your room non-rectangular! A 1" difference in width between front and back can make a big difference in eliminating a strong resonance at a particular frequency. If you can do the same with the ceiling too that's even better.
2. Double dry wall for sound isolation (both ways)
3. If height will allow, add a step at the back for back seating - improves the view from the back row. Build the back step with the center off the ground, so it touches only around the sides. See 'sound' below for reason why.
Electrical
4. Put large (2"+) conduit or multiple smurf tubes in walls to front, side, back and ceiling of room so you can relocate equipment to any of these locations. Deciding where to put your DVD player so it's accessible easily but isn't in your line of sight with its glowing numbers is hard. Don't risk being unhappy with the location - give yourself the option to moving it later. Don't forget a front-center power outlet for the Wii IR bar.
Finish / Decoration
5. Use black outlet covers and blackboard paint on the projection wall. Do not use a strong color in the room as it will color the image on screen as it reflects the light from the projector.
6. Add sound absorbing panels on the side and back walls too if the room sounds too 'live'. You can order these to size or make them yourself using compressed insulation panels and fabric covering. Fiberglass reinforcing can be used to bond to the compressed insulation providing a strong mounting point. Z-clips are the easiest way to mount these panels with no visible screws.
Screen
7. Don't over-screen the room (most people do). Check recommended viewing distance / diagonal discussions online - about 2x viewing distance to diagonal. Bigger screens are more impressive for guests but if you actually want to watch movies and see the whole thing you're better off with the right size screen.
8. Stewart film-screen perforated screen with center channel speaker behind it - looks great and sound comes from people on screen.
Sound
9. Denon -CI amplifiers are my preferred receiver because you can control them remotely using a serial or Telnet connection to easily integrate them into a home automation solution. This allows scenarios like auto-shut-off if kids leave room with amplifier and projector on, ability to turn the volume down remotely when kids have it too loud, ...
10. Mount a Clark Synthesis Tactile Transducer under the raised deck at the back. Since you built this with supports only around the edge the whole stage will be live making for ultra-realistic tank and submarine scenes!
There's many more things I could add to this topic. If you have any specific questions please leave a comment below.