Here is a design of my sump.
Here is the direct link if you have trouble viewing it.
As you can see its self-explanatory. Doesn't cost much to make and I would recommend using acrylic sheets dividers for each of the compartment.
I really like the wet/dry filtration system as this compartment doubles the wet/dry filtration of my existing Eheim 2227 wet dry filter as when the filter sucks up the water into the external filter, the water inside this compartment reduces and therefore the live rock rubble which I place in this compartment gets flooded with O2
and flourishes with nitric bateria. The water changing compartment is great too as I do not need to turn off the system when doing water change. I have a water pump with reverse flow to pump the dirty water out and clean water back into the system.
Any questions please feel free to ask.