This is a question on improving the aesthetic of my outdoor space. I did an extension panel on my cinderblock fence to help improve privacy and I'm very happy with the look. I used shade fabric that is supported with some wood and EMT piping that I attached to the upper half of the wall to make the total height approximately 8ft. My question is I'd like to run some type of strip along the wall that would sort of look like a chair rail that I'll paint a medium gray (accent color of our home to tie it all in together).
The reason why I'm asking for advice is because I live in the desert and the temps can get to 121 degrees in August. So I am not sure if lumber would be the best bet. I wasn't sure if some sort of metal flashing that I can prime and paint might be better since it won't warp. I'm open to ideas. But since I'm painting it a medium charcoal gray color I'm guessing that will also make this area absorb more of the hot desert sun. I'm just looking for something that is about three to four inches wide that I can buy in 8ft lengths or longer and attach to the .5" thick wood that is running along the middle of the wall (where the shade fabric was stapled to the bottom). Of course, something lightweight would be important. Here is a photo to help with a visual. The lighter color below is the painted cinderblock. The slightly darker color above is the shade fabric. The gray border would basically be a way to make the area look more finished: