You have mentioned ventilation twice, that we need more than you think. We bought one of those shed kits from lowes and built and 8x8 with 6' walls. We put in two 8"x16" air vents. The chickens will be out in a large yard during the day, but during the winter while there is snow on the ground I anticipate they won't want to come out that much. Do we have enough ventilation?
Welcome to BYC.
You need 1 square foot of ventilation per adult, standard-sized hen, which is best located above the chickens heads while they're sitting on the roost. Twice 8x16 is 256 square inches which is 1.78 square feet -- enough for 1.78 hens. I suspect that you have more chickens than that.
Soffit and ridge or gable venting is very popular, but snow easily blocks ridge vents. Top hinged windows are great because they protect the opening from rain and can be opened different amounts depending on the wind.
I suggest that you post a thread asking for help ventilating your coop with plenty of photos and measurements and information about how many chickens you have.