For building plans, look in the coops section at the top of this page.
How big of a coop do you need? What a controversial question. There just isn’t an easy answer to that. You can follow the link in my signature to get some of my thoughts on what might influence that. You are hitting several that would say build it bigger. In SW Pa. you are going to see some snow. Cold won’t be all that bad but heat could be an issue. Snow may trap your chickens in the coop for extended periods of time in winter so a little bigger or blocking off part of a run to keep wind and snow out could be a good thing.
You might do research on keeping ducks with chickens. Ducks tend to make a wet mess, you might be better off building different facilities for them. I don’t have ducks so I can’t give you any advice from personal experience. You might ask in the duck section.
I don’t know if you are planning on using an incubator or broody hens, but you will be integrating. That screams that you need bigger facilities. When integrating, I find it extremely helpful to have two separate facilities. That could be dividing your coop into two sections or building two different coops at opposite ends of your run, assuming you have a run. Separate facilities gives you a lot of flexibility when dealing with chickens, you never know what will happen. The second one does not have to be very big.
I’m not a believer in magic numbers for chickens, coop or run space or much of anything else. There are so many variables in how we manage them, our goals, flock make-up, climate, and many other things that there can be no one number that covers all of us. Even if I knew how many chicken would be your peak number it would be really hard to come up with a perfect size. For that many chickens I’d want a walk-in coop. You need to be able to reach every part of the coop for many reasons, that’s hard to do with one you cannot go inside with that many chickens.
Most building materials come in 4’ and 8’ dimensions. If you are buying new material you can normally reduce your cutting and waste and optimize coop cost if you work with those. From the numbers I think you are working with, somewhere between 25 to 30 plus who knows how much that grows when you start hatching chicks, I would not go less than an 8’ x 12’ and that might be tight. That’s not because of some magic square foot number but you should be able to fit enough roosts and nests in that and still give you a little room to work. You also need room outside for them at that size, the more room outside the better. I have two separate 4’ x 8’ coops in addition to my 8’ x 12’ coop that makes it much easier to deal with issues and integration.
That many chickens are going to be pooping a lot at night. You are probably going to have to work on poop management. I find a droppings board can help a lot with that, but getting enough roosts with droppings boards can take up a lot of coop space.
A lot of these space issues are more for your comfort and convenience than really necessary for the chickens. I find the tighter I crowd them the more behavioral issues I have to deal with (a good reason to have a separate small facility), the harder I have to work (think poop management), and the less flexibility I have to work on issues (could be anything). Keeping chickens should not be stressful to you but if you crowd them you increase the chance of increasing your stress. You don’t need that.
