A word on terraces made with rocks. Sand being very fine will shift easily and tend to level out. Gravel does the same, but the larger grain size means it is a bit easier to build terraces with rocks. The rocks have to be basically tight together with no openings. Silicone can help achieve this. Unless of course you find a long piece of rock sufficient on its own. But then there are the edges where it touches the tank walls.
The type of aquascapes you pictured are based on designs promoted by Takashi Amano. They are very high maintenance tanks; mega light, CO2, nutrient fertilizers every day, etc. Expensive to set up and expensive to run. If you want to read about this method, Mr. Amano has a monthly column in Tropical Fish Hobbyist magazine in which he discusses individual components. I believe he wrote a book (or several
) on his method, you can probably track it down, or info on the method, online. He also markets a range of products.
These are fine displays, works of art in their own right, but I am on the "natural" end of things, so I much prefer sik80's tank--which is very lovely by the way.