Socially, each individual bird a large flock in a large space has more ability to get away from other birds. But the sanitation needs remain the same.
Ventilation is airflow -- the openings in the walls that permit fresh air to enter and foul air to exit. This photo is from an article on cattle barns, but the principle holds.
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Have a look at my
Brooder Coop, which has 16 square feet of permanent, 24/7/365 ventilation plus another 10 feet of supplemental ventilation.
Building from scratch you can do a much prettier, less redneck job than my metal siding awnings.
Since you're subject to Nor'easter storms and other severe weather you might want to consider using a Monitor Roof or a functional cupola. My
Little Monitor Coop article includes photos of how to frame a monitor.
Soffit and ridge venting also works well -- leaving the entire soffit open (covered with hardware cloth), and installing a ridge vent. But in areas with significant snow you lose the ridge vent. As an alternative, you can put vents at the tops of the gables.
Generous roof overhangs on all sides are your best friends when keeping rain and snow out of the coop while permitting airflow. Additionally, any windows you put in should be top-hinged so that they act as their own awnings.
Thank you. I'm adding metric conversions to my article-in-progress and missed that.