Give them a coop with some room, and proper ventilation. You do that, and don't worry about them getting chilly. Australorps can handle the cold. I like the idea of getting a premade shed, and modifying it into a coop. Money better spent that way. As others have said, most of those "coops" they sell on-line are junk. You can go to Lowes. or HomeDepot, and see how those sheds are built. Get a bigger one, and partition off a section for the chickens. In the end, if the birds don't work out for you, you have a nice shed to put a bunch of your stuff in.