Fill your barrel half full of sand. If you are using a larger barrel, such as a 50-gallon drum, use less sand. However, depending on the degree of compaction desired, the soil added can vary.
Place the barrel on its side. Drill 2 holes exactly in the middle of either end. Insert the metal rod through the barrel.
Cut two 4-foot sections from the 2-by-4 board. Drill a 1/2-inch hole through 1 end of each section. Bolt the ends of the 2-by-4 boards to the protruding ends of the metal rod using washers and nuts.
Screw the third piece of 2-by-4 board to the end of the other 2-by-4 boards. If the barrel is wide enough, you can step inside the boards to pull your soil roller over the ground to compact the soil. However, if it is too small you can simply push it over the ground.