They are standard size large fowl. I know, NOT helpful, huh? But, if you go with the measurements for a standard coop, you will be perfect. You need a minimum of 18 inches above the perch, especially if they will fly up to the perch. You might want a bit more head space if you live where it can get very hot. If your perch is easily removable, you could get by with it being only 6 inches above the floor. A nest box is usually a 12inch cube, but variations of that work well (a little smaller is OK). Keep the nest box entrance below the level of the perch. If you are housing several hens, it might save more space to make only one nest box that is 12x24 inches. That way, three can squeeze in if they want. Look up community nest boxes on this site for some ideas. Good luck!