So, we're about to build a 5'x8' run with a raised 5'x4' coop over half of it, for 3 hens. The current plan is for the hens to basically spend all of their time in this set-up--that is, we are hoping that we'll be able to let them out sometimes in our yard which is surrounded by a 4' fence, but we're not counting on that (it will depend on how determined they are to escape the fence), so we want to assume that the coop/run will be their home. Since they will be concentrated on a small area, we are thinking about digging down about 12" in the run, and filling the hole with about 6'' of gravel, then maybe a layer of sand, then some organic matter on top for them to scratch and dust bathe in, maybe mulch or something like that. The idea would be to give the whole run really good drainage, so as to minimize problems with odors, flies, etc. Does this sound like a good idea? Are there problems with it? Is it necessary? Half of the run will obviously be covered with the coop, so it should stay pretty dry anyway, but we plan to leave at least a couple feet of the run with no roof over it (just hardware cloth or something), so that the hens can get some extra sun on our many cloudy Pittsburgh days. The spot where we are going to place the coop/run is generally elevated and flat, and doesn't tend to collect moisture, but we do get a lot of rain here, so that doesn't mean it won't be wet a lot of the time.