Ca. 354 kg
Nothing.480 square feet is a measure of area - not of volume. An area cannot have mass and therefore no weight.
Twenty feet times twenty feet = 400 Square feet of area. Divide by 12 to get the number of cubic feet which is 33.33. One cubic foot of water is 7.4805 gallons. One gallon of water weights 8.3249 pounds. So multiply 33.333 by 7.4805 = 249.35 gallons times 8.3249 pounds per gallon = 2075.81 pounds of water on the roof.
The volume of an area 24 feet round and 45 inches deep is: 1,700 cubic feet.
You need to provide information on the area of the pool as well.
2 feet 6 inches deep
If the circumference of the round pool is 29 feet, then the volume of the pool (area times depth) is about 267.7 cubic feet.
That's going to depend on how deep or shallow you spread it. If you spread it one foot deep, it covers an area of 2 square feet. If you spread it one inch deep, it covers an area of 24 square feet.
Square feet is an area and pounds are a weight. There is no direct conversion between the two.
40 to 50 feet
5,000 feet of water depth is about 147.5 atmospheres.
20000
Covering that area requires 5.00507794 × 1011 US gallons of water.