Cheap pen top net.

[its hilly]

Just for those of us with escapologists. Debris netting that they put round scaffolding. Around 6' to 12' wide with stitched in eyelets round the edge. Sometimes used as windbreak netting too.
It's only soft net, not plastic, but is usualy green, so nicely camoflaged.
Builders supply, or ask your local scaffolding company, cos they chuck it out when it tears, but it can still be in long lengths.

[Aberdeenplotter]

can also be in white but that is more expensive. The white is quite good to use as shading in the greenhouse

[chris]

I bought mine from ebay, and use it to net my beds off My chickens have learnt that with standard netting they can push it in to nibble the salad crops.

[Suechooks]

Another good option is Pheasant netting. Not too sure of price as I got mine as job lot with some other stuff

[roitelet]

Only problem with netting the top of the run I have found is that when it snows, and we had a lot last year, the netting holds the snow and presses the netting down so we couldn't get into the run. The solution was to put a very high net curtain on long sticks above the height of the run. So long as the chooks didn't have anywhere high to perch on inside and then fly over it worked well. I only used fruit nets.

[Suechooks]

Only problem with netting the top of the run I have found is that when it snows, and we had a lot last year, the netting holds the snow and presses the netting down so we couldn't get into the run. The solution was to put a very high net curtain on long sticks above the height of the run. So long as the chooks didn't have anywhere high to perch on inside and then fly over it worked well. I only used fruit nets.

Pheasant netting is much more open than bird netting so might be less of a platfom for the snow. Wouldn't like to guarantee it though!