Much of the P&W-RR structure is being built on a foam base and with foam incline grades. All of the products use in this particular layout come from Woodland Scenics which are readily available at local hobby supply stores. During the course of building up the layout, I'll share my experience with the use of foam and hopefully some interesting tips and techniques.
In these pictures you can see the yard shelf with a layer of 1/2" foam topped by sheets of N-scale foam roadbed. I've chosen to attempt to use the N-scale foam roadbed instead of Z-scale cork roadbed ... primarily because it is much less expensive and easier to use. In the yard area, using sheet material makes a lot of sense versus laying individual tracks of roadbed material. Actually, a good portion of the sheets shown here will be cut away as I finalize the tracks and add some beveling cuts where needed to improve the look that will appear with the addition of the ballast.
One thought that you may have is that the N-scale material is too thick and wide to be used as Z-scale roadbed ... fair enough, I initially thought that too. After thinking further I realized that I could easily cut beveled edges where I needed them widthwise and that the height disparity can be easily accounted for by not running the plaster cloth (to be added later) under the roadbed but rather up to the side of the roadbed (and taking up the height difference). Hopefully what I plan to do will be more obvious later when I get to adding the ground surface (and not a disaster in the making!:-)