Ok, basic sump with refugium - a la Ingy
Start with 3 sections. First section is where the water lines from the display tank feed. There is room for the skimmer and baffles are designed to provide sufficient room. Skimmer may need to be raised off the bottom a bit to get the right water level.
Baffles. Normally an over then under baffle pair. First baffle is glued to sides and bottom. Second baffle is about 1" further along and has a gap of 1-2" from bottom for water to pass under. This baffle pair promote bubbles to go up between baffles. First baffle determines water hieght in first section. Not terribly important.
Next section routinely houses some extra rocks for BB filtration and macro algae to consume nitrates and phosphates. Chaeto is most common. You need a simple light for chaeto. 17w CFL clip on desk light from home depot works great.
Another baffle pair same as before then the third section. This is the return section where your return pump resides (unless you want to plumb an external return pump from this section). This section needn't be too big, but all your tank evaporation comes out of this section so don't make it too small. If you use an ATO, your level gauge goes here.
Most dumps seem to be about 6-8" deep depending on sump size determined by baffle height. You should plan on having enough room for water in the sump so that when the return pump is shut off and the tank back syphons into the sump it doesn't overflow.
Baffles shod be the same material as the sump because acrylic glue doesn't stick to glass and silicon won't stick to acrylic long term.
A la Ingy version. I only have 2 sections. There is no baffles between the area where my drain lines are and skimmer, and where my rocks and chaeto are. Only a baffle pair to my return section.