In 2010 I build a planter for my carnivorous plants out of wooden blocks:
Sadly, even though I coated the inside with a thick layer of paint, the wood has started to mould because of the watering water. So now that I have an awesome 3D printer thanks to instructables I decided to build a new version.
Btw. don't worry, if you don't have a 3D printer. I am sure that you can build all the elements out of wooden blocks, craft foam, tubes and store bought figures. Or you can build my older version, just remember to properly coat the inside.
In case you are interested in the science of the self-watering planters, this is how they work:
Like most self-watering planters, this one works due to capillary forces. The cotton or wool thread we are going to use consist of many thin hairs and therefore a lot of thin channels in which adhesion and cohesion forces occur. Note that the bigger the specific surface area compared to the volume is, the bigger the resulting capillary forces are going to be. Btw. this is the same effect, that prevents the paint or water from immediately dripping from your paintbrush or the reason why trees can't get bigger than 130 meters: After 130 m the strength of the osmotic pressure and the capillary forces are not big enough to overcome gravity .