Initially I felt bad for OP that a lot of the responses were shaming them to protect their coop from rodents and not addressing the question of heat stress, but I’m glad to see all the wonderful advice. It’s like, if the bathtub is overflowing, you don’t tell someone to mop the floor, you tell them to turn off the faucet first. It’s tough being a chicken owner, especially in extreme climates such as Nevada.
Yes OP has a lot to work on, as all coops and runs are a work in progress. New chicken owners are always evolving their care as they learn more. My chicken housing situation needs a lot of attention as well, and I live in Montana where it’s over 100F in the day, and then stormy and windy at night.
My one cockerel herds the girls into the coop by 4pm, peak hotness for my area, and refuses to let them out to drink. I have plenty of ventilation, but it still gets to 95F in my coop. I’ve resorted to closing the coop so he can’t shove them in there too early. I reopen it when it starts to get dark.
I frequently replace their dustbath with cool soil/sand to dig down into, give them a constant supply of ice in their water, plenty of waterers and pans of water, filled with mint leaves and ice, and frozen or chilled watermelon, cucumbers, and leafy greens.
I don’t have misters, so if it gets bad I pick them up and place their feet in a pan of cool water, or lightly mist their feet and combs with a gentle spray, since they don’t seem to want to do that themselves.
Good luck, OP. I hope you don’t lose any more.