I suppose it would be more proper to call them range houses now, since they don't move anymore. In our old chicken tractor system, we would hook them up to our 'big' tractor and move them a full length forward every day, or every other day. This meant that the chickens inside were on completely fresh pasture all the time, leaving behind an even amount of manure. It was great for a while, but over time we realized that driving across the pasture so much was compacting the soil. Another disadvantage was that it took a long time to do the chores-you have to move these things s-l-o-w-l-y, and it required two people-one to drive the tractor, and one on the ground to watch chickens to make sure no one's toes got caught under the runners.
So, now they stay put, and they have movable fence around them to put them on fresh ground when they wear out what they're on. The chickens seem to prefer this set up. They are really quite habitual-they like to dust bathe in the same place every day, have their mid day siesta under a particular tree, etc. It's much easier to do chores and only requires one person. The disadvantage now is, the chickens stay where they are, and we have to move the manure! We fill the houses with pine shavings, and clean them out, which is a drag, but once composted, it makes a fabulous mulch/fertilizer.
As you can see in the above picture, the houses are covered with greenhouse plastic. In the winter, this provides them with extra warmth and light, and in case of particularly severe weather, the sides roll down for extra protection. In the summer though, they need the shade. I found these excellent 'sunblocker' tarps at tarps.com. They really work, are super quality, and very affordable. If you need a good tarp, this is the place, and they will ship it to you so fast you won't believe it.
In other news, Steve and crew have finished fencing off the first of our large pastures. It is ginormous.