What material can you use outdoors as a cover on a gazebo?

[two little kiddie winks]

I am building an outdoor room/ gazebo type thing & wonder what material I can use as a cover that is somewhat waterproof/ doesn't matter if water goes through just doesn't wreck it by doing so.

something like this: http://www.furniturekue.com/romantic-modern-wooden-outdoor-gazebo-by-senses/

Thanks