Even if it has one wall totally-mesh, if it were me I'd still put at LEAST some opening high on the back wall, so you can get some crossbreeze. Maybe even more than just "some", it totally depends on your typical weather and how often there *are* breezes to take advantage of at the particular site where your coop sits.
That said, if you omit it and just go with 3 solid walls and one mesh, you should still be pretty much "outdoor shade temperature", which is as good as you're going to get thermometer-wise. All's I'm saying is that on really hot days sometimes a natural breeze is good too.
good luck, have fun,
Pat