My understanding is that a rule like four square feet per bird is a bare minimum for an enclosed space, such as you might put them into for safety at night while sleeping. I also think that that rule does not scale very well, there will be so much poop, I don't see how that can remain hygienic.
Do you plan to put them away each night into these little pens? They won't go on their own, door will need to be locked.
What about preventing predators digging?
Earlier in the thread I saw the comment about 70 birds, I may not be the best person to speak to a larger flock like that. We have 3 ducks, and there is a good amount of maintenance to keep things clean and safe, just as it is with this number. We have a 24 sq ft hutch that we put them in at night, and a covered run/pen that is 450 sq ft, has a 80 sq ft pool. We will add a few more birds soon.
