building my own indoor bed

i am going to be growing in my closet, a 3x3 and 8 ft tall, i want to build a square grow bed, but i was wondering how deep should it be?

i plan on building with wood to the exact dimensions of the walls around

for plants going up to 1.5-3 ft max in flower or a sog what depth would be a bout right to allow the roots to have?

instead of using pots that are round i have the square area so i can plant more, then harvest re-clean the soil and go again.

or any other ideas to have a square setup of sorts, where i can add as many plants in the400hps light area.

wouldnt bother, it will cause no end of problems if something goes wrong.

get some square pots and your sorted
http://cgi.ebay.co.uk/10-X-5-5-LITRE-SQUARE-PLASTIC-PLANT-POTS-BLACK-NEW_W0QQitemZ130271197849QQcmdZViewItemQQptZUK_Home_Garden_Garden_Plants_Pots_Window_Boxes_CV?hash=item130271197849&_trksid=p3286.c0.m14&_trkparms=72:1296|66:2|65:12|39:1|240:1318
http://www.greenshorticulture.co.uk/subcat.asp?subcat=92&cat=22

Try orchid pellets for an ebb-n-flow grow. Not soil! Watch Mr Green's "I grow Chronic" on youtube. He discusses the orchid pellets around part 4 (its a 9 part series).