I'm getting about 40 mallard/pekin or muscovy ducks. Their run is 200x 200ft. (an area I used to start sheep is). The space in that area should not be a problem, but I need to confine them at night. I've never had problems in day time with the chickens, but always problems at night unless the chickens are in a secure koop. I'm going to build a koop (if that is the correct term for a duck house in )their 200x 200 area. How big does the koop have to be, when they are full grown? I guess the question is, how many sqft. per duck in semi-confinement?