I have built one using celotex. I used 2 5ft. 2x6's for the top and bottom. then I cut the celotex in 1ft by 4ft pieces and stacked. Then used 1/2" all thread on the sides to compress the target. carboard also works good instead of celotex. I have been using it for 4 years and it is outside in the weather all year round. 9 sheets of celotex makes a 3ft by 4ft target.