In hot dry areas, sometimes coops are three-sided, with the fourth wall made of welded wire for security against predators. The "missing" wall provides extra ventilation and makes sure the coop doesn't get too hot inside. In cold areas, they can be quite small. A coop can be a purpose-built structure or a converted shed or building, made of wood, plastic, adobe, etc. They can be large or small.
Small coop with attached run
Large coop and run
A coop can be made from brand new materials or recycled ones!
Coop built out of recycled pallets
Coops can even be mobile. A mobile coop meant to be moved every day to new pasture is often called a "chicken tractor."
Chicken coop made mobile with wheel kit
A run could also just be a large fenced area that surrounds the coop. Sometimes you might even have a mobile, enclosed run. This allows you to have a large, stationary coop, but to still move your birds to fresh pasture every day. An example of this is our Hen Pen Chicken Run below. It can be made into a tractor with an optional wheel kit, to use as just described, or they can be attached to any existing coop (and, in fact, several can be linked together for nearly unlimited run space).
Versatile chicken run