Alex, I suggest you use Suntuff Polycarbonate corrugated roofing, it is vastly more flexible than metal and you can cut it easily with a jig saw. It cannot be damaged by hail and has a long guarantee against UV damage (15 years I think). I used this stuff for my observatory roof and it has been great, allows a bit of light through, depending in what colour you choose, and can follow curved shapes provided you align the ridges with the bend. Unlike metal roofing it does not transmit heat as much. And you can buy it at Bunnings.
http://polycarbonate.com.au/domestic...ntuf-domestic/