This is a quick (not to scale) drawing of what I mean: the floor gradually slopes from the wall to the drain at about 7/16( 0.4375) inch per foot from the short sides of the wall (the 7 ft from wall to the drain) and exactly 3/16(.1875") of a inch per foot on the long sides ( the 16ft from the wall to the drain).
So the base is a rectangle 14'x32' but the shape is most related to a cone ,.... but all cone formulas assume the base is circular. I'm at a loss of how to pull out only the rectangular portion out from the middle of a cone shape. I hope this made it more visual it has 3" of Drop in the Center, length is 32' and width is 14'. just looking for a formula to calculate it. Any help in the right direction would be appreciated.