The centroid of the trapezoidal with its one face perpendicular is given be
Y=1/3 h (b+2a)/(a+b)
Where a, b, h and origin is as shown in the figure below.
Similarly, the centroid of any trapezoidal is given by
y=1/3 h (b+3a+c)/(b+2a+c)
Where a, b ,c, h and origin is as shown in the figure below.
The result was obtained using MathLab 7.0