Hi Spudcounter
Polycarbonate Sheet , not the corrugated stuff plain sheets. You can cut It to any shape. Drill and put small screws then mastic
I'd be interested to know of any advantage from using clear solid PC rather than the 4mm twinwall version (not corrugated - that's PVC and really is rubbish).
Twinwall is lighter, much, much cheaper and gives better insulation.
The only advantage clear solid PC has is that you can see your plants from the outside (and a few percent more light gets through) and looks better - at least initially (PC is so soft that it will look pretty scruffy after 1 season - it's also much harder to clean than glass).
The best solution is glass to the south and PC twinwall to the north. Glass lets in more UV for toms, peppers etc.
So if appearance-plus-toughness is the key then use solid PC for the side you see from the garden and twinwall for the rest - but don't try keeping desert cacti in there - they sulk from lack of UV.
I'm perennially irritated that clear solid PC isn't available in 1mm - because it would be plenty strong enough and I want to curve it for rigidity and use it as a clear cover on a fan peach - so I can see the blossom while keeping the rain and leaf-curl off during the critical spring period.
Acrylic and PVC are a waste of money as they become brittle in a few years.
Cheers.