[coldcanna]

Whats the current situation? You framing from the ground up or just putting equipment in a sheetrocked room? Vapor barrier is correct, sheetrock and wood will absorb moisture and make humidity control more difficult. At lowes they have the reflective backed foam insulation boards, 4x8' for $13. Or reflectex is another vaporbarrier. Duct tape everything you can. Electrical outlets are common areas for air infiltration keep that in mind.

Unless you need to keep smell down, its cheaper to burn co2 a little more often and use fans for cooling than to fully seal and do AC. Every tomato greenhouse on the planet burns co2 and vents for cooling. AC will add around 1/3 more to the cost of your powerbill whereas burning propane occasionally is reasonable.