A couple ways to approach it...
First booth position in the room. Especially if you have a stereo main mix, you want to put the booth, and specifically the sound board as close to the center BETWEEN the left and Right mains as possible. If it's not possible to get to the center, oh well-but ideally, that's what you want. Front to back, you can put the booth in the center of the room (if it's a large room) or at the back of the room, but distance from
stage is not nearly as important as lateral position.
With height, the thing to keep in mind is that you want to hear EXACTLY what the audience hears. And a sound booth that's too high hears sound differently than the audience does. However some considerations necessitate going high. It's easier to secure a high sound booth from thievery. At any rate you at least want the booth 2 feet higher than the floor so that a seated soundman can still see over the heads of the standing audience.
All that being said, my soundbooth is 12 feet higher than the
main floor because my sound booth is on the balcony. I simply keep it mind when mixing, and occassionally go down to the floor to make sure it still sounds good down there. You eventually learn how to compensate with certain frequencies and volumes.
Size: in an ideal world, the bigger the better. Consider room for the board of course, but also for the equipment rack(s), the lighting
console, computer(s), video control, drawers for odds and ends, legroom, spot to put the video camera tripod (and don't kid yourself, there will of course be a necessity to set it up in the booth). Ergonomics for multiple people to move about in it.
Power: I have quite a
bit of stuff in my booth, but I only use 2 20-amp circuits with room to spare. Might want to get a third
circuit if you have a lot of video equipment.
Materials: The more solid the better. Formica works great. Talk to carpenters about designing a booth with nooks and crannies for equipment racks and drawers. There is a certain amount of liberation about being able to climb up ON the counters with all 200 pounds of my weight so that I can get access to the back of the equipment.
Keep a 2inch hole saw on
hand for punching holes for cables and ventilation.
Oh well, my 2 cents.