I've been doing a lot of work and research on my chicken tractor in the last month. I've done far more reading up on construction and carpentry topics than I ever thought I would! My chickens will be living in their chicken tractor full-time, but most of these items apply just as much to a proper coop.
Read enough predator-related message threads on the chicken forums, and you will start to see raccoons around every corner. Which isn't far from the case, honestly! Even in the city, chickens face attacks by transient hawks, raccoons, and free-range dogs and cats.
One common lament I've read over and over is, "The [raccoon, dog, cat, whatever] went right through the chicken wire!" It's often said that chicken wire is only good for keeping chickens in - it does little to keep other animals out. Hardware cloth, which is made of welded wire in a square grid, is the only predator-proof option. Neither PVC plastic hardware cloth nor chicken wire will keep predators at bay.