If you are thinking in terms of filtration ability of Live Rocks, my advice is, DON'T!!! Our tank should be an object of beauty ... the aquascape determines the amount of live rocks, not the other way around. Otherwise, you will end up with a "shelf" design ... the same as 90% of all tanks in the world!!!
With the advancement of technology, there are ever more ways of setting up a tank ... for some of my tech inclined friends, an over OVER sized skimmer (x 3 or 4 times tank volume) ... in my previous tank, a DSB in the sump with a bare bottom main tank. In both cases, live rocks becomes a supplement, rather than the main filtration option.
Just my PERSONAL preference, I would recommend you a different approach. Most of the beautifully designed tanks are often with large open spaces and very limited amount of rocks. Consider this ...
1. Look at as many pictures as possible. Choose one design that you REALLY like. Try to avoid the typical "shelf" designs.
2. Try to adopt the design in your own tank. Use JUST ENOUGH rocks to acomplish your tank design. In the past, I used too much rocks in my tank, and it just looks like a wall of rocks!! If you keep fishes, I highly recommend an open area.
3. Once you have aquascaped your ideal tank, than plan for your filtration system ... e.g. DSB in sump, skimmer, algae filter, etc. There are so many choices out there now.
This way, you can get a truely beautiful tank, without needing to worry about how filling up your tank with rocks!!!
