You need to build the skimmer chamber high enough for the skimmer... too high isn't necessarily bad since you can put something under the skimmer like eggcrate on PVC
, but you have to leave room for water from the overflow and whatever comes out of your return line to drain back down without overflowing when the power is off.
I originally went with skimmer > fuge > return, but have since tee'd my drain and have a refugium that overflows in to my sump, increasing my total water volume by about 18 gallons. It's all personal preference. I was told that running the refugium off the return pump isn't the greatest idea, since you're essentially recirculating skimmed water through the refugium, and also possibly pods