There are many reasons for building a chicken coop but one of the most important of them is protection from predators. In this article I want to give you a list of some of the basic predators and their characteristics. Depending on where you live the predators that are most common will vary.
Fox
The fox is a crafty animal that will make a quick meal of your chickens if given the opportunity. The fox will generally stake out a coop for a short time before they actually attack the coop. Foxes are very good climbers and diggers so when building a chicken coop keep this in mind I would recommend burring the bottom of your fence a minimum of 18"deep. This depth will give you a better chance of keeping the fox from getting to your chickens. A roof is always a good idea for protection where ever you live.
Raccoon
The raccoon is an animal that can be a multiple problem predator. The raccoon has the ability to climb like a cat, dig like a dog, and it has the ability to unlatch your doors if not locked. When building a chicken coop keep the raccoons abilities in mind. A good sturdy door with a hasp lock is recommended rather than a slide bolt. I would also recommend a good roof with no openings. The raccoon will dig under your fence so the 18" rule will apply when defending your chickens against this sly animal.
Coyote
The coyote has the same hunting style as the fox they will take their time and stake out their prey for a while before they actually attack. The coyote will not climb like the fox; their entry will be from digging under the fence. When a coyote gets into a coop they will kill as many as they can swiftly and violently. If your area is dominant with coyotes, I would recommend building a chicken coop with a concrete foundation. With your wire buried into the foundation it will be very difficult for this aggressive animal to get to your chickens.
Cats
The cat is an animal you will find in most areas around the globe. The cat is another crafty critter and loves to get to your chickens. When building a chicken coop to prevent the cat from gaining entrance to your chickens a good roof and a no opening fence would be recommended. The cat is not known for its digging ability so you can bury your fence about 6" for protection cats.
Dogs
When building a chicken coop to prevent dogs from getting to your chickens remember that dogs are predominantly diggers and have brute strength. I recommend a heavy gauge fence material to protect from an aggressive pounding approach that a dog would take to get to your chickens. I would also recommend a foundation at the base of your coop. Dogs will be discouraged after awhile of digging with no results. Dogs are not a crafty animal, they depend on their strength.