One of the earliest examples of parametric design was the upside down model of churches by Antoni Gaudí.
In his design for the Church of Colònia Güell he created a model of strings weighted down with birdshot to create complex vaulted ceilings and arches. By adjusting the position of the weights or the length of the strings he could alter the shape of each arch and also see how this change influenced the arches connected to it.
He placed a mirror on the bottom of the model to see how it should look upside-down.