a simple and effective sump with refugium would have 3 sections, intake (which will hold your skimmer and heater(s), refugium, and then return.
You will want a bubble trap before the return section.
The partitions should be the height of the recommended water level for the skimmer to work most efficiently. I think about 10" is good.
I would purchase an overflow box instead of making my own from scratch, but that's just me.
Then you'll need a return pump. This must be sized with the overflow box, accounting for head loss. In other words, if you have a 700 gph
overflow box, you would need a slightly stronger pump, because you have to figure you'll lose some pressure pushing the water up and through any turns, so I'd probably want something about 850-1000 gph