We created a family in a metric generic model.
The beginning was to draw two reference planes and the adding of a dimension between them (DI). We had to be sure that its metric, therefore the parametric Modell.
The next step was creating a rectangle (extrusion) and finish the exit mode.
To lock the size of the rectangle to the given reference planes we aligned and locked them. Each one. After this we changed into elevation where we draw also reference plane. There we added the dimensions, aligned them and locked the rectangle sides.
For each dimension we had to create a new parameter. I created three: width, high, thickness.
After this you have to load them into the project. The family types can be found in the project browser under the point ,generic models'. So each family type can be added to the project.