i was lookin around skate ramp-building forums (www.rampplans.org) and i noticed that a lot of people were usng sketch up to draw plans for their ramps
i figured i'd give it a try and it turns out, although i haven't figured out the textures yet, it's quite easy to use and you can export as a 3ds
www.sketchup.com
you have to fill out a little info form to download the 8 hour trial
i'm sorry if this was posted in the wrong section