Before new construction died off we roofed year round. Some Winter months were busier than our Summer months. The last new construction rush saw my two man crew (me and my brother) with 3-5 roofs at once for all of Dec/05-Feb/06.
Last Winter we did a few new roofs.
Now with mainly tear offs we take off mid December-mid March. We got some snow and cold a couple weeks ago and have only done one tear off since. We have three to do this next month for the energy star credit and yesteray papered in a 65sq new roof, best thing it's a 5/12!!!
As far as Winter goes tried plowing but didn't like it. Rent out a sleeper fish house on a big lake on the MN/Canada border and do a lot of ice fishing. Been out two nights already and going out tommorow night again. Getting some very large walleyes.