I have 7 hens whch are housed in a coop 10ft long, 4 ft wide and 5ft tall. The coop opens to a run that is 20ft long and 15 ft wide. The run use to be way smaller, but I realized how much happier the girls seemed to be when I let them free run in the backyard. Since I have extended the run where they now stay permanently, they seem less stressed and I also keep them out of the garden...
We just built this one and it cost roughly $550 but we got the windows for free