Watercolor tip: use salt to make snow!
For the house shape (this has nothing to do with salt yet) make two angular shapes with a dark brown and a slightly lighter brown. Achieve the lighter brown by adding water to the dark brown in your mixing tray. This two-tone look adds to the sense of depth and perspective. For the snow-covered roof, use a light wash of blue to indicate the shadows of the snow. Leave some of the roof, where the sun would hit, empty (white) to make the snow look bright. For snow on the ground, use a very light wash of blue to indicate some of the shadow areas.