2 x 4 Grow Room Construction Help

I've built 2 of these, one was 6' long 7' high and 4' wide and housed 2 400w HSP's worked great (this was 10 years ago). Current is a 3x3x7 housing 1 400. I will be moving soon and planning a new room:

I plan to build it 4.5' wide by 8.5 long and 7' high (the extra 1/2 foot are so I can allow some extra grow/maneuvering space) I will be setting up 1 400 and 1 600 hps (eventually 2 600's). I've always used black plastic for my walls but this time because of the situation I will be wanting to have the room more self contained, meaning solid walls (sheetrock the best??) a ceiling in which to exhaust out into a charcoal filter and a lower vent to bring in cool air. Any advice is welcomed, if you foresee issues please let me know.

thanks

things that go BUMP in the night.....

sounds good, i would advise to use plywood instead of sheetrock though. home depot has plywood with a reflective metal surface on one side that works great for a decent price its called tek shield. the one great thing about using wood vs sheet rock is you can literally hang shit anywhere you want on wood. i built a 10x10x7' room and it came out good. i will be building 2 more of these in the next few months to run co2.

tek shield sounds great, thanks!!!