Make a grid of ropes running horizontally and vertically across the roof. They form a mesh across the roof, and split the snow into smaller sub-units. Loop the

Make a grid of ropes running horizontally and vertically across the roof. They form a mesh across the roof, and split the snow into smaller sub-units. Loop the ropes around pulleys on each side and stack some weight to keep them taut. After a snow storm, use the pulleys to slice upwards with the ropes through the snow (using edge pulleys), splitting them into square chunks. The ropes that were on the roof have to unwind to form a linked network, so they can push against the snow. Starting from the chunks nearest the edge of the roof, move them downwards off the roof, and iterate upwards. Reverse and do the same for the other side.