Shawn I wrestled with this too. In the end I went with the cement floor for a couple of reasons, first and foremost was safety. With our ground it would be nearly impossible to dig down and bury wire to make it dig-proof. Unfortunately the wildlife seems to have no problem burrowing through this ground
The second reason I chose to do the cement floor is because I am getting heat, water and electric out there and I thought a bare ground would allow the frost and cold to push up through the ground into the coop.
I have a layer of Styrofoam insulation below the pad, and skirting the perimeter of the pad at and angle to help deflect the frost away from the slab. The barn will not be warm, we are going to keep it just around freezing, any warmer and the birds will be shocked going in and out in the winter.
And yes, I do have a floor drain. You would have to check your local ordinance but I was able to do a gray water system. That is a leach field without a septic tank. But because there is no tank and no oil separator I cannot park equipment in there or pour any chemicals down the drain. It is for washing hands and dishes only (and the ocassional pasty butt) Nothing can go down the drain that isn't already laying on the ground.
I don't know what your cold range is, we generally run from -10F to -35F in the winter. And once the snow melts there is plenty of standing water till the ice goes out of the ground. Another reason for the slab, keep the birds out of the breakup floods.
Good luck,
M