Hi Smidge, I reckon the cost is about 10e per sq m as 3 pieces give 1.06m  x  1.2m and there are 7 pieces for 21e so with my 14 sq m to cover I'm hoping it works out quite reasonable. Its just a covering, no gutters or gulleys or joints so with a bit of luck it should be easy to install. I've seen it done on a " joist and batten" type structure aswell as the joists covered with osb but need to see which option suits me best. It seems to be a kind of moulded bitumin product so I'm hoping should last but if all comes to all I'll just do it with the sheets everyone else seems to use  :)