I see your name is Mac lover, so are we to assume that you are looking to build a Mac computer? If you're just looking at building a Windows PC, then what JayKay said, is basically right. If you're looking at building a Gaming Rig, then a decent case will be needed too. Simply because the type and size of the graphics cards you may want, and you may want to run a couple of graph cards in sli. Look at how you're going to keep these cards cool, such as ventilation, fans, heatsinks and/or water-cooling.
It would pay to invest in an Anti-static Wrist strap so you don't inadvertently damage any hard ware(especially CPU's).
Check out PC building forums for help