Google Sketchup is a phenomenal service. I would love to have dynamic parts in the free version, but I suppose I will survive. I use it by making geometric shapes (mostly quadrilaterals) and grouping them together.
The great thing about Sketchup is all of the measurements! So I can essentially break down various items and figure out what kind of material I need to assemble. (I did this manually though for the most part, there is probably a way to do it automatically)
With the list of items needed I was then able to make a material list for the various components.
Which I can organize by size
And then make a cut list.