How big of a screen are you going to have/want? My media room is 11'X25' and I fit a 10' wide screen in there. And we are still able to sit back far enough to where it isn't straining your eyes. Some people put a big ass screen in there, but sit like 5 feet in front of it. It is like watching a tennis match - you have to sweep your head side to side to watch the movie.
For a six person media room to be confortable and fit (2) rows of 3 media recliners you would need around an 18x12 (depending on where it door is and it if would interfere with the design).
An 18x12 would allow for 6 people to fit confortable and be far enough away to view a 106" screen. We are seeing a lot of homes being built now with this or similiar size room. If you have the option I would not go any smaller.
Got Stripes? knows his shit... I'd agree 100%, but when I have one built, it will be 18-20 feet wide and about 26-30 feet deep. I want 3 rows of 5 back, 3-4 middle and 2-3 up front, with about a 100-120 incher.