I too use sand for the coop floor, live on the south shore, Massachusetts, zone 6. Installed about a yard and a half in an 6' X 12'. Coop built on 16" X 4" x 2" cinder blocks burried in the ground. Build coop with a clean out door, outside the fenced in area to make annual turn over a bit easier. Clean the floor morning and night, very easy to manage using a cat litter scoop. Keep an old cat litter plastic pail with lid just outside the door...perfect size. Smell only becomes noticable about 3/4 full at which point it gets dumped into the garden composter. Cat scoop does miss some of the small stuff so making a sifter the size of a dust pan. One a week I sift through the top layer and get most of the droppings. Feathers collect in the coop corners and are difficult to get with scooper. Use DE mixed in. Sweet PDZ or Stall Boy would also work. Floor a bit dusty but a sign the sand is dry, odor has not been an issue. Hang herbs: lemon balm and mint. Have not had an issue with flies. In fact fly sticky strip catches very little. Considering PDZ or Dry Stall as additional mixins if experience indicates a need, particularly in winter when the ventilation is limited - windows and doors kept closed. Use large mason mixing pans under the roosts where most waste collects. Floor material, if dry should not make a difference in winter. The key to maintaining heat is the balance between protection from drafts and humidity build up/ventilation management. I have not insulated the coop, will see hoe they fare. Plan to oil combs when cold weather expected. Have a thermometer with humidity gauge that I monitor weekly. Sand covered dropping go right into the compositor or are worked into resting garden beds...the sand is actually a benefit given the hard clay soil here. The decision on flooring material is a personal preference, choose something in line with your maintainence style.