There is a lot to know on this topic, depending on how in-depth you want to go into it. The best place to start, or at least where I started, is in Soundwave's thread on RC. You could probably skip the first split if you'd like since it deals with older technology now and the implementation is essentially the same. A recurring theme is new DIYers joining the thread and asking similar questions so a lot of points are reiterated and driven home. This also allows for some skimming, which helps, since the third split has over 300 pages.
Soundwave's build thread on RC:
http://reefcentral.com/forums/showthread.php?t=1587273
There was a thread dedicated to summarizing the key points from the main one but I seem to have lost the link. Links to it start to appear part way through the thirsd split.
Also, there are a few DIYers on Canreef too, including myself. I have two fixtures planned for later this year, when I have the funds. I'd be more than happy to answer what questions I can.