Well, at least those are pretty big holes and not just tiny specks lol
But even so, you should just leave the whole space under the eaves open! The whole length of the coop. Why does he want to block them off amd leave only tiny holes? Would be easier to just leave them open anyway! Then cover with hardware cloth.
And put couple gable vents in each end.
And maybe some windows but that's optional but honestly kind of necessary.
And that is bare minimum ventilation....
2 4x15 holes are definitely not big enough lol
They say like 1 sq ft of ventilation per bird but that was one article and I think it's slightly excessive... BUT. It does highlight the need for ventilation.
In my new 4x8 coop, we left the eaves on both the 8 foot sides open, it's maybe a few inches, idk, then added a gable vent on one end, and we have 2 small windows on each side of the coop. We also just added another vent on the other end cause I insisted. My dad didn't think it was necessary but I say it is. It's not an official vent though. One wouldn't fit there cause the door is so big so we just cut a really big hole at the top and covered it with hardware cloth and a piece of lattice.
That's with 8 birds. I don't know if it quite adds up to 8 sq ft of ventilation but maybe? I am bad at math lol but that is more than enough.
We almost added a ridge vent too but my dad thought it would be too cold in winter.
On a coop the size of yours, you would need way way wayyyyyy more ventilation than that.
The hot, moist, ammonia filled air rises out the top and prevents frost bite and respiratory problems. Also lets fresh air in, which is why some add lower vents. For me the door serves that purpose lol
Ventilation and keeping dry is more important in winter than staying warm.
But I am sure you know all this already. But you are more than welcome to show it to him lol
And show him this article.
https://www.backyardchickens.com/ar...-there-and-cut-more-holes-in-your-coop.47774/
This might help too
https://www.backyardchickens.com/threads/ventilated-but-free-of-drafts.1048597/
And of course you can always make a post saying how much ventilation he wants to put and show him the replies