Oklahoma summers are the bigger design challenge for a coop, not winter. Chickens handle cold far better than heat, and a coop built with insulation in mind but no real airflow plan will cook a flock in July.
Ventilation matters more than insulation
Cross-ventilation near the roof line, above where the birds roost, lets hot air escape without creating a direct draft on the flock at night. Hardware-cloth-covered vents on opposite walls, sized generously, do more for summer survival than any amount of added insulation.
Shade before you need it
Position the coop and run so they get shade during the hottest part of the afternoon, whether from a building, mature trees, or a simple shade cloth over part of the run. A coop in full sun all day, even a well-ventilated one, puts unnecessary heat stress on the flock.
Water access is the real bottleneck
In Oklahoma's summer heat, chickens can go through water fast, and a waterer that runs dry by early afternoon is a real risk. Oversize the waterer relative to the flock size, and consider a second waterer in the shaded part of the run during the hottest months.
Don't forget winter
The same coop needs to handle an occasional ice storm and hard freeze. Design ventilation that can be partially closed off in winter rather than choosing between a summer coop and a winter coop. Adjustable vents, not permanently open or closed ones, are what make one coop work across both extremes.