I house my Peafowl in a large calving barn for the winter with 4 different pens inside it. The barn is not heat, but is insulated. I can house somewhere around 120 birds in it. The birds produce a lot of heat. On the warm days I turn on the fan to deal with the dust and humidity. When it’s -40 Celsius outside, the barn is about -10 Celsius. Most of the winter the water doesn’t freeze, but on the coldest days I use heated dog watering bowls. How big of a coop you want to build would depend on how many birds you want to house and how much room you want to give them. I let my young peas run the length of the barn and they love the space. Everyone’s facilities are different and it’s finding what works for you and your birds. I should also note that my barn has windows so that the birds keep in touch with the natural light as to not throw off their cycles.