My coop is a building that we originally had made when we used to breed dogs. We modified it a bit to better suit our birds. We created nesting boxes for the chickens a very long time ago when we used to have a different set of chickens in a different area and moved it inside one of the larger sections in the building. We split up sections so different ages of birds could be separated, and also so we could have a space available for any bird that begins acting ill to be separated. We put some tree branches inside for them to roost on.
Here is the inside, where the chickens sleep at night.
Here is the door the chickens come in through the outside:
We have multiple latches with springs to keep predators out. We put these boards over the doggy doors that used to be there and cut a smaller hole for the birds to come in and out.
I just moved my broody hen into another section of the building until her chicks hatch and get older. (They should hatch in six days.) We put a board over where this dog door used to be too, but we don't allow access outside at the moment.
In an identical section we have chicks that I hatched in an incubator until they get a bit bigger and can be put with the other chickens:
When these chicks were younger and it was colder, we had them in an old rabbit cage (which can be seen outside in the picture below) in the middle part of the building that the birds aren't allowed into. There we have a heat lamp and can keep the heat up in the smaller part of the building.
Here you can see the outside of the building: