I agree with perspextoe, the more light the better.
I have a cab about the same size as yours. The inside walls, ceiling and floor are painted white for reflectance.
The lighting I use varies a bit, but once the tree has moved beyond hatchling, I use eight 40w to as much as 55w bulbs above the plant. I built a tray that I move up and down depending on the height of the tree. The side walls have holes like you would find on the inside sides of a bookcase where bookcase clips are used to move the tray up and down. The whole apparatus is on a pulley system so that the tray could never fall on the tree which would damage the plant and may break very expensive bulbs.
Also, this tray has four holes in each corner where I drop down four more CFLs of the same wattage. These bulbs are set at different heights so that when turning the tree around the lighting will reach every level of the tree. I spend a lot of time and home so I can be here to handle the rotisserie.
I have managed three grows and I am on my fourth grow now. I just do one plant at a time as the trees that grow in this grow closet are above average. I also use a five gallon container.
Heat is dealt with through the use of a typical, cheap bathroom fan unit with an additional extractor above that fan to give it just a bit more umpff. Seems to do the job. Maximum heat in this closet at present is 79 degrees F. Daylight bulbs run a bit hotter so the temperatures can get close to 90 when in full grow mode. Right now, I have warm bulbs in for flowering.
Since this closet resides in a basement, the cold is regulated with a small space heater plugged into an outlet inside of the closet that is wired through a typical wall thermostat so that the space heater can be better regulated by a more accurate thermostat than the one on most space heaters. IOW, the outlet where the space heater is plugged only receives electricity when the wall thermostat determines that the temperature is dropping below 67 degrees F. Works great.
This closet has been modified many times and will be modified again after the grow I am on is finished. Just a few minor adjustments at this point. I'm a little too chicken to provide pictures. Maybe with a little coaxing
Hope this helps.
