I have NO flat land, everything is sloping and often rocky. From huge boulders to football size rocks. I have walked the woods in the spring before leaf out to find high areas to put the coops. Only 4-5 spots on 15 acres!! In spring a lot of water can run off the hill, feels like the Okephenokee swamp in many areas. Not good for chickens. The weather here is noticably different than WA and even the VA/TN area--definitely colder for longer, and not the high rainfall WA is noted for on the coast.
My coops are not mobile.
As of right now my coop is not mobile either. My land is flat and poorly drained with a high water table. I too have to know where the high spots are before the winter wet sets in and I am off the mark right now, So, I can't move the coop with the truck until it drys out at least a little bit. Maybe I should get some mud tires and tear up the yard! We learn by doing and part of that education is in learning your property. Good luck, it sounds like you are on the right track. I sure would enjoy looking at pictures of a monitor house if that is what you plan to build.