In terms of flexible (string-type) netting, there are sort of three basic food groups: 1) fancy expensive aviary netting (pretty strong), available from poultry supply houses e.g. Murray McMurray, Ideal, Randall Burkey, etc etc etc or on
ebay; 2) yer basic cheap garden netting intended for trellising or for keeping birds off your cherry trees (not so strong, but considerably cheaper, esp if you only want a little bit), available from garden centers and large chain hardware stores and suchlike; or 3) plastic mesh usually sold as deer fencing (fairly strong, less flexible), available from same sources as trellis netting.
The aviary netting mostly comes in 25' or 50' widths and long lengths; the trellis netting or deer fence come in various widths from 6' to 12' depending on the brand and type.
So it depends on how much security you want, and how much material, and how much price.
Note that NONE of these will slow down a possum or raccoon for more than about five seconds, and do not count on them to keep jumping dogs or climbing foxes out either. They're really only to keep chickens from flying out, and hawks/eagles/owls from flying in. Also they must be VERY STRONGLY BRACED if you get any snow in your area, and may come down despite it.
Good luck, have fun,
Pat