Building on the idea of the self watering plant pots (there are several instructables) I've built a bigger version, using IKEA boxes.
Step 1: Get all the Tools / Materials
Get some boxes. I used "Samla" boxes from IKEA because they are cheap, available in different sizes and you don't have to buy the lid (which we don't need).
You will also need some string, scissors, and your trusty Swiss Army knife. (Since you are on the instructables website I think it is save to assume you have one)