What should the size of my ebb traybe

I want to grow about 8 plants in my closet i want to set up a ebb & flow system. I have more length than with. So if any one can think of some good dimensions for the tray of my ebb system that would be appreciated.

the with of the closet is about 2 - 2.5 feet length is about 6 feet

think 2x4 would be 1 sq foot per plant. That's what I would do at least...

what should the depth be. Will this size be ok for flowering?