We do not live on a farm, nor do we want to turn over our garden to foraging chickens, so we designed a small coop with a partially covered run that nestles in a far corner of our half-acre next to “open space”. It has worked out fairly well. Had I stuck to my original plan for having four hens, instead of six, (see my entry on a “problem chicken”) it would have been even better.
When designing a coop and run for your backyard, consider this. Will your chickens be able to be outside most of the day? In our temperate climate, the hens go inside only to lay eggs or to run from a hawk flying over their pen, so inside space is relatively small. Even in the rain they prefer to be in the outdoor sheltered area of the run rather than indoors. Do you have predators that would threaten your birds, or could they free range (with only a shelter for food, water, and nesting boxes)?
According to most books, large breed hens only need four square feet of space per bird and 12″-18″ of roosting space. While this is adequate, giving hens a little more space than the minimum requirements, makes for happy layers (you know how girls are). Design your coop for easy cleaning (it is inevitable). Provide a nest box for every four hens (even at that, ours have had to “double up” occasionally during a busy spell. Consider climate, lighting, ventilation and your neighbors, when designing a coop. A little research now will make for happy hens later.