i have a small 12x12 run i use for the birds in the winter when they want to come out of the coop. it has a metal roof. the four sides are covered with chicken wire i have to shovel the roof off in the winter so it dont collapse been using it the last 3 years like this. was thinking of wrapping it with 4 mil plastic to keep the snow from coming in this year less shoveling . i heard i should keep one side open for ventilation i have a door thats 3x5 i could leave that open for ventilation. they only come out of the main coop in the winter when the ground is bare or if i put hay down . some are braver than others.