Problems with Solid Difference Tool

Thanks for the Help,

I am very new to grasshopper, be for warned, and I am running into intersection issues.  I have developed a pattern of shapes that will eventually be based off some real world constraints (solid areas for door handles etc, open for visual connection).  The goal would be to have the final panel water cut or laser etc. 

I want the solid areas to simply be shapes cut out of a panel, but as you get further from the control point (door handle or whatever) the shapes get larger until they start overlapping.  In order to maintain the shape of the panel, the larger shapes would become an offset of the initial shape so they can hold each other up (see attached file).  

Unless I don't understand the vocab, a brep is the same as surface?  Brep being a generic term for poly surfaces?  In the case of my model, I plan on using two different shapes at different scales and using the difference tool to subtract the insides and leave a surface outline.  I cannot seem to get the subtraction to work, and I get the warning that no Brep was found.  Since I am working from surfaces, how is this not a brep?  Or is the problem somewhere else in my commands?

Thank you,