Our 4 chickens are full size now and have outgrown their plastic dog house coop. We have a very large wood dog house that we're getting ready to convert into a coop. As it is now, if we put a door on it there will be no open holes for ventilation. How much do we need to provide for chickens who will be in the coop only at night while they sleep? Are a couple of small holes (covered with wire) at the top on the front and back sides enough? TIA!