For the run/pen area, how big should I make it (ft wide x ft long)? I'm assuming the sq ft per bird does not include the height. Ideally I know the bigger the better, so I'll go as big as I can with the space, but what is the smallest I could go? I would like to find a happy medium for the birds that fits with the space we have. They will be let out of the pen for 3-4 hours per day. I currently have an 84 sq ft pen for my 5 older girls (they are only 15 weeks right now), but for the most part they don't even use half of it, and when I let them out to roam they don't go more than 20 ft from it. I'm thinking of building a pen adjacent to theirs that I can open and close a small door between the two after I introduce the babies in a couple of months, that way I can keep them separate or open it up if they end up getting along. How big should I make the new pen? Or for all 13, what should the total size be? Thank you!