If they will be let out at the crack of dawn and not shut in til they've put themselves onto the roost and dozed off, all you need is something big enough to contain the linear feet of roost required (tho I would recommend being a little generous and giving them at least 1 linear foot of roost per chicken, e.g. two 16' roosts or four 8' roosts for your 35 birds). Depending on how squished you want to be *yourself* when you're working in there, that needn't be an especially large structure.
If they will realistically be locked into the house for longer than that sometimes, you'd want more room.
Good luck, have fun,
Pat
If they will realistically be locked into the house for longer than that sometimes, you'd want more room.
Good luck, have fun,
Pat