Sketchup is used mostly for architecture, but it works for 3D printing as well, but keep in mind if you make any circular or curved parts, they will actually be a bunch of lines. If your design relies on curves, 123D design is a good program too (http://download-3d.com/123d-design).
When you say your work didn't go all the way through, are you saying you make a shape to cut out but it only cut in part way? If I interpreted that right, to cut a shape out of a solid you select your sketch with the push/pull (p) tool, click it once, rotate to the other side of the object, and click on the surface of that side. If you switch to 123D, you can push through as far as you want to cut out a shape.
I think your right when you say there's no file sharing on Tom's. Also, how are you measuring how long the parts need to be?