Making "Snow" Technique #1:
On the roof and for landscaping, use "Bright White" Celluclay®. This is fine paper mache product available at craft & hobby stores. It can be pressed to conform to the shape of the roof shingles or moulded into snow drifts. It may take a couple of days to dry. Then paint it with white paint and, before the paint dries, sprinkle with "Crystal Clear" glitter.
Making "Snow" Technique #2:
Lay white felt fabric on wax paper and coat with diluted Snow-Tex. Before it dries, sprinkle with glitter. It may take a couple of days to dry completely. When dry, you can cut it into shapes to drape on window sills or lay it around the house for a literal "blanket of snow."
Using diluted Weldbond or Ultimate Glue, paint the acetate window panes and before the glue dries, sprinkle with glitter. When the glue dries, it will be invisible and the glitter will look like frost.