But if the building is not going to have heat while the work is going on, it could get VERY cold inside the building.

And if you potentially won't have water or a way to heat water, even to make a cup of tea? If it were me I would not plan on being there. Even if I wore my down parka, my boots that are rated to -40C, and wrapped myself in a down comforter, I probably could not do it for more than an hour. If nothing else I would go stir crazy being wrapped in a down burrito. 30-40 minutes outside, in constant motion walking my dog is my limit. Sedentary I don't think I'd last more than 10 minutes.

I'm sorry we're a full 3 hours away from you, because I'd offer you an air mattress and a spare room.