It forced Ferguson to think about what material properties snow and stone might have in common. Stone, for example, can carry weight. It has compressive strength. But it can't be stretched very much, so it has significantly less tensile strength. You can make an arch out of stone.
Snow has similar characteristics.
An igloo is really a system of arches. And a minimal surface can also be thought of in terms of arches. In effect, every point seems to be the keystone of a cluster of arches. Marble can be carved fairly thin. Ferguson wanted to test the feasibility of carving snow into the required shape, but there was a dearth of snow in the month of May in Maryland.