Are you talking making your own/having one built to your specs?? In which case design it to do whatever you want but simple always works best and don't forget to allow for the overflow water when you turn your main pump off lol. Then are you going for a weir or box in your main tank?? I hate the overflow box but some use it and it works fine so don't jump on me! I#ve designed and made loads of these for weir systems in reef set ups, just remember a few key points: 1 try and incorporate a sock, some love um some hateum but the fact remains it lengthens the time until you have to clean your media, but you have to clean your sock!! 2 remember flow through your media, to large a chamber/section and you can get channeling through the media, make the flow work. this means building in more smaller sections in which the water flows, but the volume of water means it has to use the full path through the media (does that sense??) Remember that you get water drop as your water travels through the sump section, allow for this or your pump section will run dry. Put some 'emergency' holes and or design separation plates in the separation plates as required, then if one section gets blocks the water flows onto the next section (by-passes) the blocked section. Thus you still have flow through the others. Even ensure your design allows for the filter sock blocking and NOT overflowing into your cupboard!! Its not as complicated as it seems, just common sense and some thinking. always think 'what if' and you'll be fine, good luck.