that sounds ok. word on the street is that 400 watt lights cover 3x3 max -if u want goodness. U really dont need it to be 6 foot tall either dude. If ur plants get too tall the lower branches wont get enough light and u will get crap buds down below. in a 6 foot box u could get plants 5 foot tall, when 3 is more than enough. I may be wrong but i doubt u would get any more yeild from a 5 foot plant indoors than a 3. If u boxed off 18 inches or so at top you could have a chamber for cuttings/seedlings as well. just some thoughts dude.....