When I built my coop, I added a vent right at the level where the two roost bars are positioned. In the summer time, the most common prevailing wind blows through this vent and (I hope) helps keep the birds a little cooler. Now that cold weather is here, I needed to block this vent so the coop isn't too drafty for the ladies. I figured out a pretty simple way to block the majority of the cold wind while still allowing good light transmission and an inexpensive price tag. I had some 3/4" square hardwood trim laying around from another project but a 2x2 could have easily been ripped into quarters on the table saw if needed. I made a frame just slightly smaller than the opening of the vent area. I glued the wood and popped it together with a brad nailer. Let it dry overnight then stretched some heavy clear vinyl, purchased by the yard ($3/yd) from a local fabric store. I stretched it over the frame and used a stapler to secure it. I then press fit the panel into place. It seems to be blocking almost all of the wind but still allows the light to enter the coop. The vent on the other side of the coop is much higher and should not cause draft for the birds so it is being left uncovered. As I know I'm not the only one getting their coop ready for winter, I thought others might like to see this or comment on how they cover their own vents if needed.