That fiber glass sheets are bad. I wanted to cover my filters with it but it is very flimsy and about R400 for a 3m sheet. Think the shading cloth will be better, or if you want to spend +-R900 a square meter you can fit a louvered roof system.
http://www.continentalproductsonline.com/prod_vergola.php
http://www.equinoxroof.com/Product.html