OK generally the sump/fuge is under your tank. Water comes down a pipe from your overflow and enters the first chamber, this is where you put your skimmer and a crash chamber if you would like one, next is a set of baffels, next is the fuge section, followed by more baffels, and finally a section for your return pump which attaches to the plumbing for your CLM. As for sizes there is no rule of this many inches for this or that section. My advise (take it for what it's worth to you) is to make pressure locking baffels (look in the diy section) and keep the skimmer/intake and return pump area as samll as you can so that your fuge can be bigger. test to make sure the areas are not to small before you put sand in the fuge. Get everthing where you want it fill the fuge with sand and rock and you have a sump/refuge.
Hope this is what you wanted.