The law requires outdoor dogs be provided "adequate" shelter in order to maintain the animal(s) in a state of good health. When the temperature falls below freezing, dry bedding is required in the shelter.
Use hard plastic or painted wood (metal rusts and conducts heat and cold). Make sure it does not leak and it faces south in winter, and north in summer.
Raise the house off the ground several inches.
Put a flap over the door (an old rug or rubber mat with strips cut vertically).
The roof should extend 8 inches over the door to help keep the rain out.
Use straw, newspaper, or cedar shavings for bedding; nail a strip of wood at the bottom of the doghouse door to keep them from spilling out. Don't use rags or rugs, they absorb water and can freeze.
Put water in a sturdy, tip-resistant bowl or bucket inside a rubber tire to prevent tipping, and check for freezing several times a day during winter.