My own homemade compost bin is easy to assemble and disassemble and works with whatever size compost pile I have at a given time. It is made of rough-sawn 1×12 hemlock boards, each 5 feet long. I cut the corners from both ends of the boards to create tabs. To keep the boards in place when they are stacked in a bin, I make the tabs into notches by screwing a foot-long 1-inch by 3-inch piece of wood across the end of each board. I make the notch slightly wider than the width of the boards to allow for some movement.
The finished boards stack tier upon tier, like Lincoln Logs. To assemble the bin, I place two boards on the ground parallel to each other. Then I slide two more boards into the notches to form a square. Each time I use a board, I put the opposite side inward; consequently, the boards have remained serviceable even after 10 years. A short piece of scrap wood held by a stake fills in the 6-inch gap at the bottom of the two sides where the boards are held above the ground.