Funny, I've been toying with building a grow box of sorts, very similar to that. Basically it would be an insulated plywood box with some kind of foil inside to help reflect the light and air seal it, and also protect from the heat of the bulbs. I'd have LED bulbs but also some incandescents or CFLs to generate heat. Would be controlled by a RPI to try to keep it at say, 25C. 16 hour light cycles then let it cool off for "night" time and then bring the heat up as the lights are turned on too. An auto water system and a live web cam could be fun too.
I made a super crude one out of cardboard but it seems the growth has stopped, I think the 1 5w light I have in there is not quite enough and it's also not sealed well enough so it is probably too cold. I think 20-25C is optimal temp for growing most things.
Depending on how far I get with my plywood box (will probably build that in summer, as my garage is not insulated so it's too cold to work in there now) I might go bigger and just convert part of my crawlspace into a greenhouse.

Could do it in the one under my garage actually, pretty sure that would survive even a tornado... or air lock malfunction.
