My friend Michelle in Atlanta built this beautiful planting box out of cedar. She claims it's easy.
There is still time (Zone 7) if you start with plants (4" pots are a good choice). The secret is to use great soil. To build box, I bought three 6" x 8' cedar boards, one 36" long treated 2"x2" deck post, and a pack of 1-3/4" exterior screws from Home Depot (spent about $30 or less). I cut one of the cedar boards into two 3' lengths (could just cut in half for a 4' x 8' box) for sides. Then cut post into 6" lengths for corners. I simply screwed boards and post together using 4 screws per corner. Placed on ground, filled with Farmer D's soil, planted plugs, watered, and 3-4 weeks later...ready to harvest!