If you're in the "no snow" south, you can get away with a bit smaller of an enclosed coop IF you leave it open to a predator-safe run all the time. So the indoor coop is basically a laying box and shelter from the rain, but the chickens can also roost outside to spread out most nights. That is what we have, but again, only works if you have a very mild winter. You still need about a foot of roosting bar per bird, but you can count the outdoor space in your sq ft per bird and have additional roosts there.
Then you'd either want to free range every day or have an additional larger run they have access to each day. The minimum I've heard is 10 square feet per bird daytime space. But more is better to avoid boredom behaviors like pulling out each other's feathers, fighting, etc.
But like others said, you are probably better off repurposing a kid playhouse, XL dog house (make sure it has a lift off roof to collect eggs), etc from a financial perspective - often larger and cheaper, even after you pay for supplies to cover openings and add nesting boxes and a roosting bar or two. But they aren't as "finished" looking as the prefab coops.
You can also look on local social media for chicken groups ans often find people who build custom coops. You'd likely get a MUCH better product for not much more money.
