I think the "traditional" sump design is
1st chamber for water in, second chamber for refugium, third chamber for return pump. You can put filter sock and skimmer in the first chamber. macroalgae and live rock and/or deep sand bed in the fuge, and ATO in the third chamber. heaters can go in any.
Usually people incorporate a 3 baffle bubble trap between the second and third chambers. Water goes over the first, under the second, over the third.
So, excuse my drawing, lol
Pretend all baffles are of equal height, though they don't have to be. The height of the final baffle before the return pump chamber will determine the height of the water in your sump (important for your skimmer). You'll want to make it high enough for your skimmer to reach it's optimum level (your skimmer should say what this is). You can always raise the skimmer up on a stand if you need to but you'd have to make new baffles to make the water deeper. Evaporation will be noticeable only in the 3rd chamber. You also don't want to make your sump so full it can't handle the drain from the DT when the power goes off.