As someone whose farmyard looked like a shanty town with coops made from old fireguards through pallets to puppy cage panels to house poultry through last Winter I'd not dismiss anything as a building material. If you're talking about a low coop on a solid sheet of flooring and a lift-off lid roof and some kind of secure door for night-time, for hens that will free range during the day, then why not? The coop will have a huge footprint for the size of accommodation but, again, why not? Just be aware it will absorb a lot of heat in the summer and also need a gap at the top to allow air flow through.