Gravel and chicken manure is not a good combination because the poop goes down into the gravel and stinks every time it gets wet. Also, chickens like to dig and scratch and the gravel hurts their feet.
Can you get them onto grass and dirt instead? They'll eat the green stuff then you add litter...
OK, you still need to open up top level venting because the windows on that are at roost level and don't provide airFLOW. Installing top-hinged windows as high up on the gable peak as you can manage -- remembering to think in square FEET not square inches. Here's a good example in an article...
This one?
That coop has no meaningful ventilation since the only windows are right at roost level. :( You'll need to open it up at the roof level to create airFLOW.
Height is good, if only to avoid such things as I experienced last summer: https://www.backyardchickens.com/posts/24739256...
:frow from Moore County.
Here in the Steamy Southeast you'll do best with the most open structure possible so it's likely you'll need to add ventilation -- which is usually one of the easier alterations. :)
My experience is that I need double or triple the suggested 1 square foot per adult...
Welcome to BYC. Where in general are you? Climate matters so if you put your location into your profile people can give you better targeted advice.
For a first timer with chickens it's probably better to have no males at all. You *might* get a good one, but it's more likely that they'll make...