There are very few magic numbers associated with chickens. We keep flocks with entirely different make-ups (roosters and hens), different breeds, different climates, and different management techniques. Is it any wonder that different people need different things?
Nobody ever complains about having too much room once you get by the cost o0f building it. I strongly suggest going as large as you can afford. You’ll be happier in the long run. I find the more space I give them, the less hard I have to work and the fewer behavioral problems I have to deal with. Also, extra space gives me more flexibility when I have to deal with a problem. if you ever want a broody to raise chicks with the flock or want to integrate new chickens you will really appreciate the extra space.
In Florida you have some huge advantages. Cold is not your problem at all. Matter of fact, heat is your enemy. Heat will kill your chickens. They’ll think your coldest temperatures are refreshing. Something about them wearing a down coat all year.
One thing to consider is that you need to protect them from predators, especially at night. Whatever you do, you need to be able to stop raccoons, possums, foxes, skunks, dogs, coyotes, and who knows what else from getting in. That means you have to cover the run if you do what I suggest, since many of these can climb.
What I suggest is that you build an open coop. I don’t know what direction your winds normally come from, but put a wall across that end. Let’s just say it is from the west so I have a direction to talk about. Build a wall along the west end that will stop the wind. It doesn’t have to reach the ground. Build a short wall along the north and south side so you are forming a pocket to keep the wind from hitting them directly when they are sleeping. Put a roof on that end too. I’m not thinking about cold here but your thunderstorms and hurricanes. Just give them a protected place they can get out of the worst of the weather. Put the roosts in that pocket.
Build the rest of your coop and run out of wire. That can be a lot cheaper than wood.
You can either close off the coop portion only with a roof and such that is totally absolutely predator proof, or you can try to make your entire run predator proof and not even have an internal wall to form a coop. Even if it is out of chicken wire, I’d still put in an internal wire wall so I could lock them in the coop portion if I wanted to. You’ll probably appreciate that added flexibility at some point in the future.
Chicken wire will not stop many predators. As a minimum I suggest 2” x 4” welded wire for your walls. That will stop practically any predator you are likely to have. Hopefully bears are not on your list of possible predators.
I’d further suggest two enhancements. One is to put an apron around it. This is where you lay about 18” of wire fencing horizontal around the coop and run and attach it to the bottom. You don’t have to bury it but a lot of people take up the sod, put the wire down, and replace the sod. That gets it out of the way of weed whackers and lawn mowers. The idea is that a digging predator goes up to your run fencing, starts to dig, hits the wire, and does not know to back up. By attaching it to the bottom, you also prevent a predator from just muscling her way under the bottom of the fencing.
I also suggest taking chicken wire and putting it around the bottom 18” of so of your run fencing. That prevents predators like raccoons from sticking their through the 2” x 4” wire and grabbing parts of your chickens. It also keeps your chickens from reaching through the fencing to eat grass and exposing their heads to predators. Yeah, they’ll do that. It also keeps baby chicks from going through the fencing if you have a broody raising them with the flock.
When you are designing it, remember that most wooden building materials come in 4’ and 8’ dimensions. Why cut 2’ off a 2x4 or a sheet of plywood so you can throw that away to get a 6’ wide coop when you could have made it 8’ wide with less work and no more expense?
The wider it is the more it takes to support the roof without it sagging. You don’t have snow and ice loads to worry about, but wind can be pretty vicious on a solid roof. I don’t know your space available but 8’ wide is probably about all you need where you are going to cover it. Just make it long.
Hopefully you can get something useful out of all this. Good luck.
