So as others have shown, I have various nested generic model families, dropped them into a plant family template. This family is then nested into another plant family. This is then placed into a project. Using the height parameter in the family, changing this, scales the family.
Revit : Scaling families – #empirebim
In brilliant form, he then describes how you can use an instance reporting parameter in a Curtain Wall Panel family to drive the Height value in a nested Planting family, making a Curtain Panel that can scale its nested geometry to any panel size.
To save you some time and trouble, I have created a template for this scenario. Basically, it is a Revit project file that contains the Curtain Wall Panel family with the fully nested setup already in place. I also added a Scale Override type parameter in the Curtain Panel family that allows you to globally adjust the scale of the resident geometry.
Download the project and family files here
(the project RVT is Family Scaling Template - GM to Planting to Planting to Curtain Wall Panel.rvt)
Note: using a shared Generic Model family will not work (it breaks the automatic scaling ability of Planting families)
Looks like original credit actually goes to Kelvin Tam.
Original credit for this general idea goes to Marcello (I think), and partly to Dave. It is definitely one of those hacks that is getting re-interpreted and expanded upon as it gets blogged and reblogged...