You're right - that IS sheetblock - and it's not cheap! But I wanted to do things as right as possible. Plus I figured with MY building skills, adding a little extra sound block protection definitely wouldn't hurt. It's absolutely amazing how involved something like this becomes, and how much learning is constantly being accomplished. I'm lucky I knew how to work a cordless drill before taking this on, but now I can also work
a sabre saw!
Seriously, I've relied on a lot of help from friends - and I've paid some pros on the things that had to be pro done and I couldn't scrimp...like insulation, sheetrocking the ceiling, electricity and the HVAC.
You asked for some details, so here goes. I totally gutted the existing structure of walls, carpet, etc so I could start with a blank room. Being an old factory, nothing inside was straight (as you can tell from the support beams in the pics), so it was a challenge. I started with steel studs. All the outer walls are actually built a foot away from the real outside walls (which are cinderblock with boarded up windows) so I have a 12" gap around my total area. The control room is 2 layers of 5/8" sheetrock (the fire code stuff). I put in a raised floor for about 2?3 of the room where the equipment will go to allow for cable runs and cable access. I had all new electricity put in throughout with isolated grounds in every outlet in the CR (but not in the rest of the rooms - I just couldn't afford it). I DO have separate circuits for just about everything though. I built two walls between the CR and the live room with 8" of space between. The live room wall also has 2 layers of sheetrock with one layer of sheetblock between. Each iso only has a single wall, but double sheetrock. The wall insulation is 3" thermofibre and the ceiling is 2 layers of 6" thermofibre. The HVAC system is all new. The original building only had old steam pipes running through it and a giant fan to blow heat - both very noisy. I had everything taken out and had a new heating unit put in the basement. The HVAC guy made all the ductwork to fit where I needed it to go and he insulated it both inside and out to cut down noise. The central AC unit is outside the basement.
The doors I bought at a bargain outlet nearby (mistake) and they've been nothing but a PITA! They're steel, solid core pre-hung doors, but because I bought them at a bargain place, I must have gotten seconds or something. No two of them were the same width or height- give or take an inch - but an inch is a lot when you've already got the framework built and the walls up! I've had to deal with some major gap problems. I'm hoping my solution works so I don't have to kick myself for trying to save a few bucks. For those that don't know differently...do not EVER scrimp when it comes to doors! I know that now!
As for glass, I'm still researching. I need some large pieces (two 4' X 8' for the CR and two 4' X 4' - one for each iso). From what I've found, I guess insulated (layered) glas is the way to go, but 1/2" or thicker is not only expensive...but VERY heavy! Anyone have any other ideas? Has anyone ever worked with thick plexi? I've never heard of it being used in a studio, but I've never heard why not either.
So, that went longer than I thought. Did I miss anything? Sorry if I bored you. I'm on my way over there in a minute to get more stuff done. The small things never seem to end! Thanks for all your interest. I'll try to post more pics of the progress as it happens.
Rick
Ha! I like to see how people build their rooms.....er throw their money in the pit. 
Thanks if you can get to it.
Hence my attempt at HR type design. Besides, it depends on the type music, your tolerance for noise intrusion into the recording, and how loud your local noise floor is.