My parents ran a chicken smallholding for several years in the 1950s and Dad built all his poultry sheds using 2" x 2" for the framing and tongue and groove cladding. A shed doesn't have to be anything special. He got day-old chicks delivered in a cardboard box (with breather holes) on the train from London.
As I remember, Dad embedded each corner post in concrete, waiting a day or so, then added cross pieces, then finally nailed on the cladding. Felt was used for the roof. It was green and had a sandy surface. Crikey! My memory is better than I thought!
MM