I use Onduline for the roof on mine, its a bit more expensive but should last much longer, also it provides shade in the summer.
The frame work on mine is all wood, tanalised for everything coming into contact with the ground and I use weld wire from Hills of Devon, about the cheapest and really fast delivery.
As regards the base, again I have weld wire going 6inches down and comes out 24inches to stop anything trying to dig in. Below is a photos to give you an idea when we were building it.