*Warning : You are starting with a lot of flexibility in building room before setting up the HT, so you need to acquire or assemble the budget, creativity, artistry, knowledge, patience, labour in good measure. Its going to be a long/hard journey but the end benefits could be phenomenol in comparison to most others.
I have asked some of my friends if I could share drawings/pics when I helped them build some rooms and I wil put it up here once I get the go ahead.
In the meantime, here are some teasers.
Layout :
As the saying goes, measure 10 times and break/cut once. So you need to put some plans in place for the room such as nicely rounded walls and placement on paper (visualise amphi-theatre for a bit and model it similarly)
Seating :
with 8 people, you need 2 or 3 (preferred) levels of seating thats graded (typically with a single 1/3 - 1/2 foot step platform with the 2nd and 3rd rows following a curved sitting pattern. Build each of these platforms with a wooden base and fill them with insulation.
Seats could be 2/3/3 or 3/3/2 if the step is higher. If you go 4/4 you need a rather large size room.
Wiring : Prewire using conduits for a projector based system as Cranky has suggested. Projector should be off the ceiling with a dedicated HT rack in the side or back of the room that holds all your coponents. Always go for a bigger sized conduit and put in additional cabling than necessary for future hookup (eg. 2/3 HDMI connectors), digital coax, toslink etc.
Run subwoofer cables to all 4 walls (no I am not kidding). Ideal locaiton is middle of room for single. If you go dual, you can put them on opp walls (front/back) in the opposite corners to nullify the dips/peaks in the freq. response.
Speakes should be on a raised platform as you have graded seating. Center should be behind the screen with height aimed at the chest a person in the middle row(if using perforated screen) or above the screen angled towards the users if using DIY (read below).
Good speaker gauge (16 AWG) with quality cabling. Dont scrimp on the lengths.
Electrical : Run multi-gang power outlets that can handle US rating (20 Amp loads on a dedicated circuit).
Screen : If you are lot into DVD watching than TV, go for 80-100 inch screen. Get a ready to assemble screen or build one using frame and blackout fabric; like a canvas. Paint with Goo Systems digital grey.
Let me know if this coversation is making sense and then I can talk about the remaining like brass traps, speaker selection, ..