Step 2 in making a parametric shelf was creating a cutout template of all the pieces. I realized very quickly that it would be easier to generate the template with a separate Grasshopper Definition that referenced the input geometry and parameters, rather than trying to dissect the pieces being generated at the end of the "Model" Definition. Before I got into the nitty-gritty of grasshopper, it was really helpful to sketch out a diagram of what I was going to be generating.

It took a few tries to work out the most efficient layout with no waste material and fewest duplicate cuts. With this arrangement I can add as many shelves or dividers as I need just by duplicating the respective dotted box. Then I started scripting in grasshopper:

In all honesty,  this script was easier to write than the Model script since it was essentially just numbers. I've also been reading through Grasshopper guides, which probably plays a role. I was also able to add a parameter for a toe-kick, the lifting of the bottom most shelf off of the ground. I decided to make this parameter a drop-down rather than a slider since there are some standard sizes. Below I've paired the two definitions together on one box to show how it all works. I haven't tried updating the Model definition to incorporate the "Kick" input.