How would i power it? thanks
From the questions you asked it seems you have some studying to do before you attempt a DIY light. Look for posts by a RIUer named Rasser. He can show you how to power LEDs with a computer power supply and other more traditional ways. Offhand the line of Cree LEDs you want to use don't cover the 660nm spectrum which is a very important spectrum for LED growing so you would probably have to find a LED that covers that spectrum and works with the Cree line you want to use. Also don't get too hung up on Cree. They don't even acknowledge LED growing. Companies like Osram and LedEngin make great LEDs for growing and don't break the bank. And remember while the coral guys know their LEDs, their purposes and needs are diferent than ours. They love their Royal Blue LEDs, but too many Royal Blues will stress the shit out of most cannabis plants.
Hopes this helps you out and Good Luck!