For each adult, standard-sized hen you need:
4 square feet in the coop,
10 square feet in the run,
1 linear foot of roost,
1/4 of a nest box,
And 1 square foot of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.
While these are *guidelines*, not hard-and fast rules, there are a number of times when you need more than these minimums and being in a climate with severe winters is one of the most common of those reasons:
https://www.backyardchickens.com/th...ave-more-than-the-minimums-for-space.1462570/
Here's a good article on the space topic:
https://www.backyardchickens.com/articles/how-much-room-do-chickens-need.66180/