I’ll give you one big piece of advice here from the start: don’t do what I did.
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See the fatal flaw? Yeah, they had full access to the whole rest of the barn. Awful idea to leave it that way even if it wasn’t for very long. I was still finding eggs for years after.
Eventually I went to Lowe’s and bought some window blinds to block the open space where the majority of them were roosting in that photo and put some leftover hawk netting up to keep them from flying over.
I mounted scrap wood inside on two walls to act as equal level roosts and put up three plastic wall mount nest boxes.
Unfortunately I don’t have any other photos of what it looked like after those upgrades, but I can say it was the best coop I ever had and I would definitely do it again.