Tank to Sump Ratio

[jords]

Going to be building my new tank from the ground-up (starting with nothing but glass). Just wondering if there is a special tank size to sump size ratio? Or just whatever fits? For instance, I'm planning a 120 gallon tank. So how big should my sump be? I'll be posting a tank journal as soon as I get started, so watch for that (tips for anything is more than welcome!).

To be honest, I've never had a sump before. However, I've only run nano tanks. So with a big tank like this (which will be set up for corals, fish, and live rock), what kind and size of sump will I want? Thanks in advance.