Do you think 1/2” plywood is sufficient for the walls? Painted or stained exterior for finish. Or does it need to be 3/4”?
Our most traditional, walled coop has T1-11 with barn paint.
Hardie-board is pricey, but exceedingly durable.
Best consult shed-builders in your local area to see what you've got to contend with -- wood doesn't survive well here in the Steamy Southeast between the carpenter ants, the termites, and the wood-destroying fungi, etc.