As I mentioned in Purist's thread about track design, I think I have found a way to implement elevation changes into our SketchUp designs.
I'll try to walk you through my way of doing it, my suggestion is that you read this while looking at the different pics in the attached pdf and maybe trying it yourself in the software. It's not that complicated, it just takes time.
I don't think this is an optimal solution, but it works and isn't to hard to perform. Although, you'ld might get a bit frustrated when finishing up the track and realising that you want to revise a part of it ...
Note: I will not deal with how to make elevation, as SBF has provided a nice tutorial for this. Also, you might see that details change between pics. This is due to the tweaking that needs to be done, and/or SketchUp not being interested in collaborating with me. Nothing that will alter the process, though.
Now on to the tutorial!
1: Make the surrounding as you want them to be, don't bother about the track at the moment. I just made to circular hills to show how this can be done.
2: Make a flat plate above (or under, if you prefer) your elevation. This will be the base of your track design, so any area constraints will be implemented here.
3: Design the track, having both 2D and 3D layout in mind. You'ld might find the X-ray option (View-Face Style-X-ray) helpful here. Make sure that you are happy with your design before entering next step, because to my knowledge, there's no easy way of fixing your mistakes from now on.
4: Delete the parts of the track plate that you don't use, and extrude the track design through the elevation plate. It will look wierd, but just keep your hopes up and we Will get a nice track in the end ...
5: Select the whole model, right click and go Intersect Faces-With Model.
6: This is just cleaning up unwanted faces and lines. Since you have intersected the two models, your elevation layer now has the track design projected onto it. Therefore, you can delete the track design extrusion. Just make sure you don't wipe anything important in the process.
7: The end result, before materials. Sometimes SketchUp will get a bit cranky saying that some flat surfaces aren't actually flat, just try to triangulate and delete the diagonals afterwards. Someone might have an explanation why SketchUp is doing this, I have none.
8: Add materials and buildings as usual in track designing. Run-offs will need to be on your extrusion, or be extruded in the same way at least.
9-10: Just some pics to prove that there is an elevated track in there. My elevation wasn't really extreme, which might have been better for teaching practice.