I would make 2 nests for those hens, about 18 inches wide and 12 hi and 12 deep. Chances are they will only use one nest anyway. Put about a 2 inch piece accross the front to retain the bedding. I like my nests at floor level..........Pop
2 nests is probably a good idea, but honestly, I'd only make one. As Pop said, they likely won't use the other, anyway. If it is 18" wide, which I think is a good idea, they will go in there two at a time, anyway, if nature calls.