I saw plans for a worm bed that looked interesting. Check this site... http://www.ecoyardfarming.com/ezwormcomposter/
The great thing is this system makes it easy to harvest the worm poo.
I liked the idea but I'm too cheap to spring for the plans he sells.
So I started drawing circles on a some scrap plywood I had and found that a 28" circle with aprox 17" loped off the bottom and 10 1/2" off the top would fit on a 48" piece of plywood.
The box can be as long as you would like. Mine is 24"
The two sides are 16"x 24"
Bottom is 21 1/2"x 24"
Top 17 x 24"