That is a very good question. To begin You need to ask yourself several questions. What do you want to keep in the tank. sps lps softies clams anemone fish only. Then how much room under the tank do you have. Do you want a intank or external skimmer. Do you want a internal or external pump. Are you going to incorperate a refugium into your sump. All of these and more will effect the final design. My advice is pretty simple. Ask people to post photos of thier sumps. Look at them, at the tank, and ask what would you do differently if you had it to do over. I will post you a photo of mine. If I had it to do over, I would of used a asm g-2 skimmer. I would of had the sump drilled and used a external pump, I would sectioned of a part for a refugium. I hope this helped you in some way. There will be many more answers with better shares as you become more certain of the type and method you want to design you sump after. Steve I also added a photo of a friends life reef sump system. Very nice/Very High dollar.