Here is a brief look at my set up it too is a metal shed. You may find thinks here helpful or not.
For along time I used heater tape around a bucket with chicken watering nipples. It worked excellent. However me being me I neglected to change the water as often as I should. This is what it looks like and it thermostatically controlled to come on at just above the freezing temperature. You would have to wrap it to suit your particular application if it is viable for your set up. It is available at Home Depot in Canada.
Last year I switched to white rubber contains the wife found somewhere. The freeze solid every night but the ice just pops out of them in the morning and I replenish them with fresh warm water. They have black ones at the feed store that are similar but large than mine.
The chickens congregate around them like people having their morning coffee. The only draw back is my yard is pepper with small ice bergs the size of the buckets.
April looks after that however..
My Coop is a salvaged 4x8 metal shed here are a few tips and a quick look at my set up.
My floor are planks with a layer of tin for rodent proofing. On top of the tin I have a piece of vinyl flooring cut one foot longer than the length and width of my coop (roughly). Six inches squares are cut out of the 4 corners of the vinyl flooring. This allows the friction fitted flooring to travel up the walls six inches around the perimeter of my 4x8 salvaged metal coop. Shovel out the heavy stuff into a wheel barrow. Pop out the vinyl flooring hose it off pop it back in.
I have used all types of litter for coops.
I have not tried sand (sand gets good reviews on this site).
Of all the things I tried to date wood pellets have been the best. (I tried wood pellets as a last resort when pine shavings were not available.) They are super absorbent and swell up and eventually turn to saw dust. The droppings just seem to vanish and turn to dust when it comes in contact with wood pellets .
Replace my litter and clean my coop every October after I harvest my garden.
Works for me in my deep litter method.
I do add to pellets from time to time.
I have anywhere from 10 to 24 birds housed in my 4x8 coop.
Through the winter months the pellets froze harder than concrete with -40º temperatures. The poop froze before it could be absorbed by the pellets and there was like a crusty layer of poop in certain areas where they collectively took aim (no smell, messy feet or flies @ -40º). I frequently would just pick up a slab of poop and toss it into the composte bind during these frigid temperatures., Come April things started to look after themselves.
In my nest boxes I fold a feed bag to fit (nest boxes are 1 ft³). When a bag gets soiled; fold a new one; pop out the soiled; pop in the new. Feed bags are a nylon mesh bag frozen poop just peels off in below freezing temperatures and just flakes off in summer when left out in the sun to bake and dry.
POOP BOARDS are the "BEST" addition yet. Handles well over ½ of the poop in my set up keeps ammonia smell in check 3½" below roost excellent for catching eggs laid through the night (roost are in cups for easier removal and cleaning). I recently friction fit a piece of vinyl flooring over my poop board.it makes clean up even easier; Pop out; Scrap; Hose; Pop in.
Winter months even easier flex over compost bin DONE!