Here is what I do with my two shed coops in the winter (keep in mind here in the Pac. NW it is rain/fog, rain/fog, rain/fog most of the winter- if I go outside I can get soaked from the fog walking around my yard):
SHED #1- Metal shed with large fowl: uninsulated, condensation dripping constantly from fog all winter from ceiling and walls, rain pours in the edges/sides on the floor, well-ventilated and air fresh all year but WET. No drafts. Sand on floor. They get a 100 watt bulb for 3 hours a day in the morning to add daylight. When it dips to the 20's I add a second 100 watt bulb that runs all night (rare here- maybe 2 weeks a year). This is simply a windbreak coop. It is the same temperature inside as out.
SHED #2- Plastic shed with tiny (Nankin and d'Uccle) bantams: double wall insulated, wet in winter with leaking water around edges and damp walls/ceiling from fog. Well-ventilated and air fresh all year but WET. No drafts. Sand on floor. This coop is warmer. You feel the warmth when you enter due to the insulation. I have a thermocube in here that turns on a 100 watt bulb when it goes below 35 degrees. I run a second 100 watt bulb when it goes into the 20's.
Oh, and there is a nasty wind too sometimes, as they are at the top of a hill.
My bantams will stay in the shed all day when it is bitter outside. My large fowl wander around outside even in very bitter cold weather (20's). Our winter weather is usually in the 40's and 50's during the day with 30's at night or so, sometimes warmer at night than that.
My one pound bantams would suffer tremendously in the metal shed and my large fowl would be uncomfortably warm in the plastic shed with the light on.
Go with your gut as your coop's microclimate might be different from someone else's- and most importantly, your chickens become acclimated to your climate. A large temperature drop suddenly might be very dangerous for them, especially if they are wet. But hey if they are used to the climate and have a dry coop then that's different.
Boy do I wish I could keep a dry coop. I'd have to run a dehumidifier.