I use chicken wire, have had it on one pen for 4 years , my free range birds get on the pen so i can't use netting like some folks but i love the chicken wire.
PS i purchased more chicken wire for my other pen and it cost 45 dollars for a 36 by 150 foot roll
I have chicken wire on the top of my 40' x 30' chain link pen with the bird house enclosed. So far all of my birds are safe and none of the have gotten hurt. Since I increased the size of the pen my peafowl fly all over the place!