I have a 4-part assembly in Solidworks that is causing me problems. The fact is that I have 1500x1500 plates at the base and I use a plan to carry out my extrusion on the height. What I would like to do and that I don't get is that if I modify the plane (so my extrusion) my folded sheets are put back directly on the end of my plate.
If I understand your problem correctly, you should be able to link the dimension of your sheet metal to the dimension of the plan by the bier of an equation in the assembly.