Before the paint
Scrape, sand the worst, knock down the dust. You cannot paint over peel and call it done.
Barns and outbuildings. Paint that takes Kentucky weather.

I start at the weather side. Scrape the failed coat. Prime the bare wood. Then the color. High walls get done off a lift, not a ladder off the truck.

The last coat and the trim. Eaves, doors, the boards around the loft. A barn looks finished when the edges are done, not just the big walls.
Scrape, sand the worst, knock down the dust. You cannot paint over peel and call it done.
Primer where it is bare. Then the color. Two coats on the south and west walls.
I paint on a dry stretch. Dew and rain ruin a coat. The paint has to cure or you are doing it twice.
Tell me the building, the height, and the color that is on it now. I will tell you what it needs.