My friend Erik Knutzen of Homegrown Evolution wrote a short article on the important things to keep in mind when designing and building a henhouse and a chicken run. He knows what he’s talking about and the information he provides is essential for backyard poultry keepers.
My four ladies sleep in a hen house that is a 4-foot by 4-foot foot waterproof wooden box with a tin roof. I use high quality (dust free) wood shavings on the floor which I clean out every week, depositing the litter into a compost pile. The hen house also contains a nesting box that I built myself out of plywood. Check out some nice plans for nesting boxes here. Mine is 12″x12″x12″. Chickens like a tight space to lay their eggs, so don’t make it any bigger than that. Plan on having one box for every four hens. The nesting box should be kept full of straw or wood shavings. Ideally the nesting box is inside the hen house–hens like a dark, secure place to lay their eggs. In cold climates you will need to insulate the hen house well and keep their water from freezing.
How To Build a Backyard Chicken Coop