Hardware stores carry some good materials. Back in the fencing/roofing section, look for long corrugated vinyl panels that are used for roof-overs. I decided to go with these panels for my new pheasant pen. The 26" tall x 8' panels came in white only, and cost $13.65 each at Lowe's. 26" tallx12' long cost $20.48 and come in several colors. They won't allow airflow, but won't retain heat like metal. The price isn't bad, and they are readily available in case you need to replace one down the road. Hope this helps.