Hi Heabow

In my opinion I would go for twin wall/clear mixture. Clear polycarbonate will have some 85-90% light transmission, twinwall, depending on thickness is around 70-80%.

So if you use clear for the walls and twinwall fr the roof then that will allow some inbuilt shading from the hottest summer sun. Plus of course in winter it's better at retaining some heat.

Scott

many thanks