from 4 co-ordinates find out x-distance and y-distance
like if given 4 co-ordinates on 4 corners are (x,y) (x1,y1) (x2,y2) and (x3,y3)
x-distance = x1-x or y1-y
y-distance = x2-x or y2-y
now for area you need l and b so
l = x-distance
b = y-distance
and area is = l*b
thats all
for experiment purpose this can be done.