The weight-per-unit-area of a shingle is dwarfed by the amount of snow it takes to affect a roof.

These shingles weight 1.8lbs per square foot when installed (3 packs for 99.9sqft at 62lbs per pack). Call it 2lbs/sqft with nails. Ice (the densest form of “snow” weighs 57lbs per cubic foot. 57 divided by 2 gives us a factor of 28.5 to divide into 1ft (the height of 1 cubic foot) to find that a 1/2" layer of ice weighs more than shingles per square foot. I’m not going to worry about the weight of shingles.