A common way of working in Rhino, at least in early design stages, is to perform a bunch of boolean subtractions on a simple mass. I've created a Grasshopper component called "Carve" which makes performing subtractive boolean operations in Rhino much quicker and easier to iterate.
The component asks for original geometry, geometry to use for the subtraction, and the layer name for baking the new geometry (this must match an existing layer in the Rhino file). The component automates the subtraction, and resets itself anytime the user moves the subtraction geometry in Rhino. It moves the result off to the side so a user can operate by moving the solids on one side, and immediately see the result of the subtraction without having to turn off any layers or hide geometry.
This component relies on the baking functions built into the Human plugin. Download that at this link: http://www.food4rhino.com/app/human and follow the installation instructions on the food4rhino page.
To install the .ghuser file, in Grasshopper, select File->Special Folders->User Object Folder, and drag the file into that folder. Then, restart Rhino and Grasshopper.