Canvas(or Cotton Duck) will breathe, while coated fabrics will not. A Canvas wall tent with a coated synthetic fly might be a good choice. The fly should have a few inches clearance above the canvas to allow air flow. The fly should have some overhang on all sides, possibly more on the front of the tent. White is a good choice for letting sunlight in, but not such a good choice for UV resistance. I don't know how long the fabrics would last in the sun. Coated canvas tarps seem to last a couple of seasons, maybe more.