I used PALRUF PVC Roof Panels from Home Depot.
You can also get them at Lowe's, under a different brand.
These are the clear wavy ones, which were about $15 each, for the 8 footers.
Just search either site for PVC ROOF PANEL
I drilled pilot holes, and used fasteners shorter than the suggested ones, because it's PVC, not metal.
You have to check for spots they might get out. Video footage helps. We bought a home and moved, and I am currently using a low voltage electric wire at the top of my new fence, but one cat still got out, because the wire only sends a tiny shock every second. Definitely wasn't my first choice, but we had to get something up very quickly, in order to move them.
The first one is similar to one I saw that used round aluminum rollers at the top of the fence...
• Bengal Kitten vs Oscillot Cat Contain...
Bengal Kitten vs Oscillot Cat Containment System
This second one, simply uses netting, at an angle...
• Cats on video trying to escape Purrfe...
Cats on video trying to escape Purrfect Fence
Blacky climbing over fence, thwarted...
This will keep the cats in, but I will have to put more plastic panels on the other side to help keep the raccoons out, but that's a whole other challenge, because raccoons can find many other way in. Worst case: I'll cover the whole thing with string netting.