I have a 45 tall tank. It's got quite a bit of lr, but because it's so tall, it's hard to stack the rocks so high w/o risking an avalanche of rocks. So it looks bare. If you were to add more, you can make the base wider so you can do a taller pyramid, but glue the rocks together. For my 125g, I'm going to be holding the large rocks together by drilling holes and holding it together w/ pvc. My lfs does that to their clients' tanks when aquascaping...that way it's less likely to collapse, but not permanent.
But I really like the layout, w/ the open "common area" in the middle.