So many people on this site will tell you to buy a box from a vendor. I never took that route myself and even built the box for my first system. A box is the hardest part of the build if you have no clue what to do buying suggest reading and trying your own. Worst comes to worst , your out 30-40 bucks, not bad.
If you decide you want a box from a vendor I suggest @double 07 ; Brian makes some beautiful enclosures.