You don’t have inclement weather where you live? I’m In GA, and we have Wrath of Dog thunderstorms here. Yeah, chickens need a covered space to hang when whatever happens.
I’d still go with 12X6, and although they free range there will need to have access to a covered run for times they can’t go out.
Mine have a covered run that could be larger, I had to round them up today because there was a massive hawk circling our yard looking for a chicken dinner ☹️