A lot warmer :lau
His roosts for the chickens are wide enough so they can cover their feet with their feathers, he did not have any issues with frost bite. My chickens which are in a house were a little bitten by it.
Yes he has a roof also. I like his set up and am thinking of make some like the myself.
I grew up in Canada and 0 Celsius is 32 F so I might think your chickens should be fine.
I think it would depend on how cold it gets. I have a friend and he has open coops by that I mean nesting boxes with chain link around them and a roof and tarps for wind protection. The temps this winter got down in the teens F. The chickens did great he has been keeping them this way for years...