Speaking from experience & received lots of help from folks here in the forum ... Put windows in. We have a 10x12 shed & during the winter time it was fine but when the Florida heat hit ... it was as if I was cooking my birds.
Rodney cut out two holes on the side of the shed. He then used wood to create a frame, added wire & screwed it into the shed. (that's woman lingo btw) We have two on the side & on the upper back has a vent hole where we have a small fan blowing air out. we will be putting in two more windows on the back part of the shed this weekend.
With the storms lately, because we have the shed around a lot of trees, there is no rain going in but a mist from time to time will sneak in. The chickens do not mind.
Before the winter gets here, Rodney will be adding a hinged "door" on the frame of the windows he placed in. We'll be able to shut them as needed or leave them open but that's a future plan.
Seriously ... I'm using a shed right now ... add the window ventelation or your chickens will die. There's no other way to say it. It's a cooker in there without them & still heats up with them. We have a fan inside & will be adding a mister soon enough to the run.
Julie