one gallon weighs about 9 pounds give or take.... an inch deep by one foot by one foot is .036 pounds
An inch of rain over a surface 1 x 100 feet would be 3.6 pounds. a roof with surface area of 2000 square flat feet would be supporting 7200 pounds over its surface.
It takes an inch of rain to create a foot of snow.... In general terms I know.... I imagine it packs down as more snow accumulates.
The deal is while its on the roof that roof can support alot more than you think one square foot at a time. Its the supporting structure that needs to be able to hold that weight.
Past poultry: Buff Brhama, EE, Barred rock, Wellsummer,
Bantam mixes, Araucana, Turkeys, & Guinea Fowl.
Future poultry: Guinea Fowl, Sumatra, Wellsummer, Muscovy
"A dream without a plan is just a wish" Katherine Paterson