I built a 20x 12 chicken run out of 2 x 4's and chicken wire. The vertical 2x4's are grounded 18" deep and cemented in place. I want to do a roof. I was going to run a few 2x4's across the top to attatch the chicken wire to (and I wanted a bar to hang something from as well) but I'm worried that the wood will provide more stress on the structure than support. This is the most ambitious thing I have ever built and frankly I have no idea what I am doing. The walls have been triangulated for support. Suggestions for roof?