Well, I would start with the biggest rocks you have. Get those on the bottom and start from there. Don't be affraid to lean rocks against the back wall of your tank, could help you out with different angles for pleasing look. After that, get creative! I've rearranged my tank three times and am now finally happy with it. I'll be honest, when I first opened up my shipment of LR
and saw the one piece that was as big as my chest...yeah, I had no clue what to do with it. Just take a step back and imagine what it is that you want.
Fiji rock isn't the most flat rock in the world, which is what you seem to be looking for. If that is what you want, why not chisel away at a piece of LR
to get the shape you want? If that isn't what you are looking for, have you looked at caribean LR
? It has more of a "ledge" look that you seem to be looking for. Easy to check some out at my tank showcase if you want.
Summary - get creative and just start stacking. Can't know what you can and can't do until you try it out.