If you built your own house and you are not new to growing, why didn't you build a secret room with massive dimensions at least 12x12ft?

5.5 L x 2.5 W x 7 H is adequate, I have battled with similar and much smaller spaces though I used only HID 250W HPS. I had to mount fans, ducting and 2 blowers in the Low head-room which wasn't very helpful while moving pots around. My preference now is the entire space of a master bedroom. Current crops are throwing of dank nuggs in our master bedroom setup. Climate is easier to control and access is easy. Providing your controlled environment is perfect your bud should thrive in any given space.

I'd only evey use a small space in future for mothers and clones.