It also depends on if you let them out to fly, want to breed them, what breed and how big the flight cage. I also found that you can have alot of space but if you dont have many individual perch spaces they wont be happy. Some breeds are more territorial than others. I have found that Spanish pouters and bigger breeds claim a larger than normal territory. For example I had a 4ft by 4ft coop that housed three pair of pigeons (non breeding) easily, bu the same coop was too small for more than one pair of spanish pouters.