Here is a diagram of the sump I put together. Don't laugh at the pic. I just made it in paint and I am no artist.
Water goes in chamber one from the tank. Also in chamber one is where I keep my skimmer and phosban 150.
Water goes through the baffles.
Water goes into chamber two...the fuge that has chaetomorpha, LR, and LS in it.
Water goes into chamber three...the only point in the system that shows the evaporation that is taking place in your entire tank/sump system (so make this chamber big enough). This chamber has the pump back into the display tank.
So, this is how I made mine. There are other disigns that have the fuge seperate or have the return pump chamber in the middle and require just a bit more plumbing. This was my first and it works well (especially since I am not a DIY guy).