I really like my outer orbit 72" fixture, comes w 3x250w 10k MH and 8 39w actinic t5's.
I priced the good retro kits and would have only saved a couple of hundred bucks by building.
your gonna spend $750 for a good 3x250w halide retro kit (like a icecap kit).
Then figure in your t5 retro kit, then figure in cost of lumber for canopy (if you dont already have one) and figure in your time.
I got my 72" outer orbit fixture for 1175 shipped to my door and absolutely love it, my one shroom rock has only been in my tank for a month and they have already doubled in size from when i purchased them, coral growth is great, by brain coral has swelled up like a pumpkin.
As you can see i cant say enuff about the outer orbit fixture i have!