Coop too hot or cold question??

Hi all,

We're in the process of building our coop and wondered how do you know if the coop will be too hot in the summer, (not enough ventilation etc), and then too cold in the winter, (too much ventilation)??

I want everything right before we go and buy our birds then find we're always changing/adjusting the coop.

my hen house has a roof that lifts off and i wedge it open to ventilate when nec, it's nice to be able to take it off completely when the girls are out to give it a good airing too