p.s. if it were me i would have the elctrical (ballasts) out of the built room for a few reasons
1. keep overall heat down in the box - ballasts create a good amount of heat
2. easy access - during your plants dark cycle it would not be good to open the box and let light in if you ever needed to access the ballasts or any of the wiring
3. combination of the first two. if you ever had a problem with heat and somehow things got started on fire the box would be separating that fire from your plants giving you more time to put out the more easily accessible ballast and or wiring fire.

just a suggestion