im thinking about making a small grow box for about 3 plants maybe 1 foot x 2 foot x 2.5 feet high. how long will i need to grow the plants before i start flowering them so that they dont get too big maybe 15" high?

Depends on the strain of plant you are growing, the conditions it is growing in. Way to vague.

bigbug maybe? i mean can you let the plant grow as long as you want and then flower it? can you suggest a kind that stays small that i can order from nirvana?

I would start flowering 4 to 6 weeks after starting them. If possible get some clones. They are have the size of plants grown from seeds and are the same age as their mother. I wouldn't grow in a cube less than 4 feet high and 2 feet deep(from pass experiments) unless you use clones.

lets see. 2 1/2 feet high- 1'for the light-8" for the pot=10" for the plant. you better start flowering the seeds.

LOL...i would like to see someone flower seeds...lol