The bottom layer is the baseboard made out of chipboard, I used this because it was cheap and easy to use. Though it is worth pointing out that it can warp if not supported properly.
The next layer up is the screwed up paper balls which were dipped in a mixture of PVA and water. These were stacked on top of eachother against the facia which was in place at the time, I kept squashing them down to make them compact and strong.
The top layer or ground level was made from a pulp of toilet roll, PVA and water. As toilet roll is ment to be biodegradable it breaks down easily in the PVA and water mix to make a pulp. This was then put ontop of the paper balls and the top smoothed with a knife. It takes a while to dry completely as for the first few days it is still relatively soft, but after a week when it is fully dried out it will be very strong indeed. I can illustrate this with the video below.
<img src="http://www.flaxengaterailway.co.uk/construction/hardlandscape/files/hard_landscaping_oldlayout.jpg" alt="" />
You can also take a look at this article in the hard landscape section of the site.