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Question

A roof of a metal building has the dimensions shown below. the owners are interested in collecting rainwater falling on the roof. Determine the minimum tank size (in gallons) required to old all the rain falling off the roof when it rains 1.25 inches.

the dimensions of the building: 25ft/25ft/50ft

Answer 1

Assuming that the dimensions are l/w/h, the only dimensions we care about are 25ft and 25ft: the height of the building matters not a bit.

Assume also that "1.25 inches" means 1.25 inches per square inch of ground.

We'll also assume that the answer should be in U.S. liquid gallons, each of which is 231 cubic inches.

The roof of our building covers 25ft X 25 ft = 625 square feet of ground.  

There are 144 square inches in every square foot, telling us that the roof covers 625 X 144 = 90,000 square inches of ground.

If 1.25 inches of rain falls on each of those 90000 square inches, the roof will collect 112,500 cubic inches of rain.

The tank size in gallons is:

(112500 in^3) / (231 in^3/gal) = 487 and 1/77 gals.