What would you suggest

I am going to buy a complete hood systems with 2 250 MH bubls and 2 PC actinic bulbs. How would you suggest to set this up over a 120 gallon tank? I have a setup now on my 120 gallon tank but its a retro fit kit that fit into my canopy. This one is the full setup hood and the only thing over the top of the tank now is glass. How would you set this up over the tank, would you hang it or just sit it right on top of the tank?
 
Top