[mseepman]

When you look at the sizing for a sump, you really need to make a few decisions first...

a) What skimmer will you have? In-sump or external?
b) Will you incorporate a fuge in the design?
c) How much will the display hold, so that during a power outage, your sump can handle the backflow until your siphon break kicks in.
d) Will you have an ATO system?

I'm sure there are even more questions, but once you answer these, it will help you figure out size. If the skimmer will be in-sump, how big is it and how much room will that compartment require. For some reason, the return area reflects all the evaporation in a reef setup, so if you make that area too small or don't have an ATO to refill it all the time, then you really risk going dry and burning your return pump out.

Though it may sound complicated, sumps really do help as they add water volume to your overal project and that means you have more room for error in everything you do.

I hope that gives you a starting point.