Grow Box and Smell

This prolly has been discussed before, however I need some help.

I need to keep some chronic, when I replant and put indoors, into a closet, where I gotta' keep the stink down..

I can vent at night, but can anyone help with a good construction of a Grow Box for a smaller closet?? I have a 400 watt HPS bulb and ballast.
To hold about 2-4 plants, and is Fire Safe?

If you know of another thread that has this same info, please post it here so I can check it out.

also.. Approx. cost to build a box?

Thank you in advance.
Eveyone here seems pretty cool with help and advice. I appreciate it..

i believe to keep the smell down an ionizer would work, pretty sure thats what some1 told me