There is a distinct advantage to living on the side of a mtn as far as drainage. Pens don't stay muddy for long, that's for sure, no standing lakes. Sometimes, I'd love to build on level ground-the bantam coop we did was on probably the most level ground available for a coop build and it was quite a bit easier, but we still used the trusty level for it, since there is still the slightest slope there.
One reason we moved the pen on the original coop after the addition to it from front to back was the earth-moving abilities of chickens. They'd scratch dirt down the slope and it would pile up against the front of the coop. What used to be a foot off the ground is now only maybe three inches. We had to remove some trim at the bottom of the coop because termites took hold behind that trim, with dirt and leaves a constant issue against the building. (hint: Orange Guard, natural insecticide sold by ACE, will kill termites, smells great and will not hurt chickens-trust me, we know from experience). I always said they were trying to bury the building and no amount of raking could keep it free of leaves and dirt for long.
Now, with the pen behind the coop, down the slope, leaves from the oak trees and dirt the girls scratch up pile against the fence, which is another issue, threatening to buckle the fence. We have a cable strung on turnbuckles from tree to tree, going through the top of the fence to hold it up. Eventually, we'll have to open the bottom of that fence and rake about 3' high piles of dirt and decaying leaves out of the pen and down the slope.
That huge pen behind the coop is about 2500 sf of pen space and they still decimate it!
Edited by speckledhen - 1/30/12 at 5:16am