Many pergolas are left open to the sky, and any plants that might grow on top of them provide the only cover. This can be beautiful in the summer months, but many homeowners find that they want something that offers more protection, made from sturdier materials.

Metal

Metal pergolas tend to be the most durable and more permanent structures compared to other pergola materials. The roofing can be easily cut and shaped to any size, and commonly used materials include aluminium, tin and steel.

Fibreglass and Plastic

These transparent or translucent materials offer an excellent compromise between an open topped pergola and a covered one. You can still enjoy the sunlight without letting in harmful UV rays, and rain is also not a problem, so you can enjoy your outdoor decking space all year round.

Fabric

An alternative cover to use is fabric. Fabric can  provide protection from UV rays, which will help to keep your outdoor furniture from becoming faded. Fabric also leaves you a lot of freedom with regards to style, so you can add your own individual flair to your pergola.

Source: http://madisonboswell.hubpages.com/hub/Pergola