How to install corrugated plastic roofing sheets via WikiHow. Low cost roof sheeting at http://www.roofinglines.co.uk/products/?s=cast-iron-83-profile-11mm-thickness&utm_source=pinterest&utm_medium=pinterest&utm_campaign=pxpinterest2.
A clear plastic roof may be just what you need. You can get clear corrugated roofing at your local building supply store or try something a little different. The material in this photo is 1/2 inch thick honey comb plastic from Tap Plastic. I think it looks a little more upscale and diffuses the light nicely.
I like the idea of using corrugated roof with clear - so light can get in... but I guess it will depend on what material it is? I am happy to clean it every so often - but will need a ladder!! Like this shape and simplicity..