Absolutely no offense to your tractor, but if I could roost in a big airy barn or the dark shelter of that tractor (because I don't see any window-like openings in the top part), I'd opt for the barn too. Can you frame in/wire in a stall for them in the barn, so that they'd be more predator protected?? You could cut a pop door in the external wall of that stall. Four foot is a pretty high jump for breeds like orpingtons and such - maybe a chicken ladder leading up to the roost or nest boxes??? I don't think the cold will be a big issue inside the barn as long as you could provide a draft free area with boards, tarps or stacked hay bales. Just my 2 cents...
