Advice for 250 Watt HID Grow Box.

I would like to start a grow, and I plan on spending a lot of money for this grow cab, so no ghetto stuff. I need help with ventilation and design. How much ventilation will I need? And I need a solid design. I was thinking 3x3x2 Box. First insulation, then reflective mylar. How do I keep this box cool with a 250wt HID?
Thanks a lot for any replies.
Peace and Love.
-Brandon.
 
Top