Assuming the local axis Y of the building is vertical (most cases), a way to compute the cosinus (named “cosp”) and sinus (named “sinp”) of the rotation angle of the building around the vertical is the following:

        local q = self:getOwner():getGlobalOrientation()
        local sinp = 2 * q[4] * q[2]
        local cosp = q[4] * q[4] - q[2] * q[2]

Note: You can check that cosp*cosp + sinp*sinp is near 1