Building in the elements during sub-freezing temperatures comes with challenges.  The obvious challenge is the safety of the crew.  The crew must protect themselves from frostbite which means either wearing heavier boots, thicker or layered clothing, or taking many more breaks.  Thicker clothing is a concern because they reduce movement and gripping ability which in turn is another safety concern.  Wearing boots when they are used to shoes increases the chance of tripping and stability is reduced ascending ladders and walking on roofs.  Stepping away from human factors, compressed air, used for pneumatic tools, creates moisture which can easily freeze in the tank, lines, and tools.  Equipment using engines may be difficult to start if they start at all.  I could keep going if I start talking about materials issues… but I’ve run out of space.  Bottom line: building outside in very cold temperatures is not very safe or productive.