Well, I wasn't on the forums too much when my dad and I did his theater in his new old house. There was a relatively decent room in the basement for the theater application. Really, the only negative was the 7' ceiling. Since it was an older house, it had a brick fireplace and wood paneling on all of the walls. Also, there was no framing on what was to be the screen wall or the right wall, just some wood paneling nailed directly to the foundation...weird.
I helped him rip out all of the paneling and then I moved to California. He framed up the front wall in a standard fashion and framed out the right one with 1x4's to prevent having to move the heater. Then he did similar over the fireplace after sealing up the damper and packing it with insulation. He also put a header in and made the wasted space under the stairs into an equipment closet. He wired three new, grounded 20A circuits for the room and put in some can lighting and sconces. I think I helped with some wiring before I left, but I can't remember too much about that, other than the HDMI cable being just barely long enough.
He built a riser (filled with insulation). The hot water heater was in the way but he just trimmed the casing and built around it, with a vent in the riser for heat, as you can see shortly. I don't have any pictures of all the construction business, just pictures of after he was done with most of the room...
Right side of the room facing the screen wall:
Left side of the room facing the screen wall:
Riser:
Cabinets housing Cat5e wiring for the rest of the house and future snacks and such:
Under-stairs equipment cabinet:
Here's the vibration-damped projector shelf I designed. It has rubber grommets on the shelf and the frame so the shelf is completely decoupled from the frame. It is also lined above with acoustic panel material to absorb any extra sound:
I will go hunt down more photos now.