I went to restaurants (chinese are best) and asked for old plastic buckets. Don't use the ones that contain paint or contstruction spackel, they leach plastic.
Food grade works best.
You can find how to put it together on the intertubes.
This one is crude, but you'll get the idea!
You'll need a wicking device (a cup with holes in it), a tube that reaches from soil level into the water chamber, and a screen to keep dirt above the water chamber.
Don't forget to drill the weepholes just below the dirt/screen line.
I have used them for 5 or 6 years, mostly for growing tomatoes and peppers. I use a home-made version. You can find lots of designs on line. The potting mix is more important than the design of the box. Use something based on fine pine bark pieces. Mixing your own will save you more than a few dollars. 8 years? A mix that lasts 8 years? I doubt it, especially if you plant the same type of plant each year. I replace half the volume every year with fresh mix. The discards get spread onto other parts of the garden or the lawn.
I have 3 Earthboxes, which are self-watering containers, that I use to grow peppers, cherry tomatoes and lettuces in. I use them to supplement my main garden - the peppers appreciate the added heat of a container, the cherry toms can be replaced as the vines die and don't take up valuable space in the main garden and the lettuces can be moved in and out of the shade which means I can grow them almost year round. They're great for just about any veg that grows above ground, but I wouldn't use them for ornamentals. Similar styled self-watering containers would work though.
With an Earthbox the potting mix can be re-used for up to 8 years (don't ask me how they came up with that number!) - it just needs fresh fertilizer added each time a new crop is planted. And a whole crops fertilizer is added at once. They are a bit expensive though, but the pros out weigh this IMO. Typically any other plants I grow in containers drown or just languish.