I built two bins so I can keep finished compost in one while the other is still working.
Step 1: The design
I'm providing the .skp file in this Instructable. Free! as in free beer. NOTE: after download, you must rename it with an .skp extension for SketchUp to recognize it.
Step 2: Gather materials
2 x 4, about 24 linear feet
2 x 8, about 35 to 40 linear feet
5/4 x 6" decking, about 40 linear feet
1 x 1, about 40 linear feet (I ripped these down from extra 5/4" decking, but you can buy them at big box)
3" deck screws, a small box
2 1/2" square drive, composite deck screws, a couple small boxes
6 galvanized tee hinges
36" wide fiber glass netting or hardware cloth, about 25 linear feet
Rubber spline (if you're using the netting), about 35 feet
The lumber I used is pressure treated with the less evil kind of micronized copper preservative. You would definitely not want to use lumber treated with the older chromated copper arsenate, which has been known to leach into the compost.