A 400w HID covers 9-10 square feet...if you put it on a light mover, you could do 3-4
but I would try 2-3 at most, because during flower they are going to spread and take alot of room...what are you starting with?...clones or seeds...clones you might be able to squeeze 4, but with seed, you have to determine sex and cull the males, so be frugle with your 1st grow