Step 2: The Self-Watering Planter Box
I built the planter entirely out of scrap wood I had saved from past hauling jobs.
There was nothing particularly fancy about the design.
Long straight flat piece of wood, screwed into an upright piece of 2×4, shorter flat piece screwed into the 2×4 at 90 degrees from the first one. Just a plain rectangular box, with no bottom.
I made 2 layers of wood on each side, for strength and stability. Some of the scrap wood wasn’t wide enough, so I used two boards, top and bottom, [on the short sides, picture 2]. I put on some particle board shelves on the outside [on the long side, picture 3] cause they look better than the scrap wood I had.
(The half barrel in the pictures is from a hauling job; it is not in use yet.)
I lined the bottom with old carpet (also from a dump run) to protect the plastic which goes above it (the plastic left over from a furniture move done in the rain). [pic 4] Then an old blanket on top, both to protect the plastic and to aid in water wicking.
I placed some pieces of broken concrete as supports, and on top of that a sheet of peg board, which elevates the soil above the water reservoir but still has good drainage.
The theory of a self-watering system is that the water below is accessible (via soil wicking) because the soil in some spots dips into the reservoir, but it does not saturate the soil or plants because the majority of the soil is out of the water. In this way it simulates ground water and keeps the soil just slightly damp at all times, but never soggy.
In my system the peg board does not fill the whole planter, so the central area is above the water, but the soil on both sides can reach down into the water pool. 
The mesh keeps the soil from getting into the reservoir.  it is held in place temporarily with duct tape, but the weight of the soil itself should hold it in place once it is in.
NOTE: In a proper, traditional self-watering system there should be an overflow port and a fill tube. I was aware of this when I built mine, but didn’t bother. I figured I could always add them in later if need be, and i was lazy. So far, as you can see in the last pictures, the plants have been doing fantastic with my extremely haphazard way of watering: Every once in a while (maybe once a week) I feel an inch or two into the soil. If it feels dry, I add water from the barrel for some more or less random amount of time, (usually until I happen to remember I left it running).
My watering quickly became much more haphazard – closer to once or twice a month. Apparently the large water reservoir system actually worked, because nearly everything survived the summer – and the winter. Even the annuals!