That's a really broad question.... what are the dimensions of the tank, how high would they hang above the tank.... did you want a DIY or a retail LED setup.....
Kinda like asking what size car do I need.... the devil is in the details
With a tank that size you could grow anything you want with 24 to 36 three watt emitters and have more par going to your corals than if you had 250 watt MH. and no heat to boot