The National Film Board of Canada produced this video (originally on film) in 1949 to show how igloos are made in far North Canada.
Using hard-packed snow, two Inuit men skillfully build an igloo as an overnight shelter. The operation takes roughly 90 minutes while their sled dogs patiently wait outside.
The video shows how the packed snow is used as building blocks. All the snow is taken from inside the circle, so the floor is much deeper than might be expected. By cutting the first row into a sloping shape, an upward spiral can be created. Interestingly, the right handed builder works counter-clockwise while a left handed one would work clockwise.
Nomadic Inuits would make igloos as temporary homes. They could take as little as 40 minutes to construct, using only a knife. When the home gets dirty or hunting becomes scarce, they can easily move on and rebuild.