I recently tried my hand at using Google's free SketchUp software to make some 3-D renderings of the Dunes Junction Layout. Mostly, I'm using to figure out my scenery and structure placement. Here's my first cut.
My one hint for anyone who wants to use SketchUp to plan scenery and the 'look' of things is to work in full size rather than in miniature. In other words, my 5' by 1 1/2' layout became a 444' by 130' layout.