It used to be the only way you could really get a decent LED setup over your tank was DIY.. that is not the case anymore. I would actually be as bold as to say that you would be better off buying a few Radions or AI Sols instead of DIYing it all. With these fixtures, you get the added bonus of having a light that works with controllers.
I've done the DIY thing and it's definitely rewarding, but when you factor in time spent, cost of materials, and headaches trying to fix problems that come up, I don't think it's worth it to DIY anymore.
Oh, and if the cost of the ready built LEDs is a turn you off, factor in 10 years of replacing MH bulbs every 6-12 months. Most of the time you'll break even with that alone, not even counting the electricity savings (efficiency, no chiller needed, etc).