We have an open bottom coop design, our coop is about 40" off the ground, double doors in front, just 30" deep and another 40" ht. The bottom is covered w/ hardware wire, 1x1, and we have just 5 ladies. Most of the droppings go straight down to the ground, which in about 2 hrs will be sand again - going to get a ton of sand in a bit. Our run / yard though is completely enclosed and we lock the ladies up tight at night. We live in Berkeley, CA, so we may get frost but almost never gets to freezing and this is at night, not during the day. The ladies are so cozy in their coop I have no concerns about warmth. This is a design that is popular in our area so we just copied it. The sand run though I learned about here and it has worked well, save our recent flooding however we got almost a foot of rain in 6 days. As soon as it stopped raining the run has dried out nicely and I have made some drainage changes and added a new roof covering to ease the weather. I did not do that from the beginning b/c I wanted them to have as much light as possible. I will add a gutter system too, but that will be in March I think - we joke we should sell our eggs for $1 million each b/c it feels like that is how much it costs to get each one! We also need to change our foundation, as we have been treating for rats as well, though that does not effect our actual coop design at all.