Ugly? You should see mine. Well, maybe not if you think yours looks bad.
That does present a challenge but you are just looking at stopping wind blowing rain and snow in. That should make the front easier. It’s not like water is running down to it off the roof.
The beams up top look like 2x4’s? My thought on the front is to take another 2x4 (or whatever it is) and cut it into a fairly sharp triangle. A really short piece. Screw one into the ends of each of those beams sharp end up. Drill pilot holes. The lower screws might need to be fairly long, depending on what angle you choose. Then put a strip of material, maybe plywood, onto those to form an awning. Since it is at the top and water will not be running into it, you don’t have to seal the top. Keep the opening pretty small but a slight gap, maybe 1/4”, will probably do you no harm. It does not have to be a perfect fit.
Your sides look a lot like the open side on mine that does not have an overhang. These are probably the ones causing you the most problems. That looks to be maybe 12’ long? Anything you put up there needs to be supported pretty well or the wind will just blow it off. I don’t have any great ideas there. Maybe build a covered panel a couple of feet wide where one top board screws into that top beam and you have knee braces going down to the studs on the coop to support the outer edge? A version of this would be to build that panel so it sloped down at an angle to form an awning and the knee braces go horizontal into the studs. Sounds kind of complicated but it could be done.
Something else that might work. Look at Home Depot or Lowe’s or similar stores for some type of awning that can be put up there. A cloth or plastic awning with metal supports that can just be screwed into the wood. I don’t know how expensive that might be or how well they will hold up to a really strong wind, but they should be pretty quick and easy to install front and sides.
If you have the same ventilation on the lower end where you have overhang that you have up top, closing off the sides may work. Just cover them up. If you do this, I’d cut another ventilation hole down near the bottom with a flap that can be lower to cover it in the winter. I’m thinking a hinged piece of wood that can be raised in the summer and lowered in the winter. Put this on the shady side, probably the north but the east isn’t too bad. With that open in the summer you’ll get relatively cool air coming in to push the hot air out of the top. I’d worry more about ventilation in the summer than winter in Ohio.
With decent ventilation a little occasional moisture in there isn’t the end of the world, but with a wooden floor you don’t want it to stay wet enough long enough to rot. It looks like a really well-built functional coop other than rain coming in. In your winters you’ll find that snow goes in there too. Not just when you have a strong wind to blow it in, but one of those snows where the light flakes are kind of hanging in the air and gently swirling. That’s when I normally find my coop floor white.