For the walls, should i use flat white paint or foil tape? I've had good times with the foil tape in the past but i'm afraid of heat issues.
I am building one too, I will be using Mylar to cover all interior walls, I would avoid using foil...
I would not use foil tape. I would paint the walls gloss white and Leave it at that. As far as heat issues I can't say right away. What lighting and Wattage are you runnin? HID, fluro? I've never used them but I've heard LEDs are good for keeping the heat down but Most ppl I know only use them for supplemental light to an already existing HID. You might look at gettin an air cooled light. It won't cut the heat out but will help
Flat white paint is the best material to reflect and refract the light inside your cab. It's easy to apply and inexpensive, it doesn't fall off or rattle or get tangled in fans. The "color" white that our brains see are a result of the fact that it is reflecting all visible spectrums of light at once. This is nature's reflector. If you choose to use a film, you can use mylar (not foil, it will retain and reflect a lot of heat/cause hot spots) Or you can use Panda Film (or Orca) These are white fiims which are better than mylar in my opinion. I have an 8x10 grow room, which I have invested in heavily and everything gets hit with flat white paint, because I've found it to work the best. It's insanely bright in there.
I think most (if not all) white paint is pigmented with titanium dioxide. But I'm no paint expert. =) Check out the roof coating paints. I used an elastomeric roof coating to paint my entire room, and it's unbearably reflective.