yea, DIY. When choosing a sump, you should also have your protein skimmer selected. The skimmers are different sizes (both on area needed and hight.)
You'll need to make your first sump chamber big enough to hold the skimmer, and if you look at the skimmer specifications, it will say how deep it can be (ie. sit in 8" of water.)
You'll probably need to make a little stand for it to sit on (I did this out of a piece of plexiglass with 4 legs cut from PVC pipe and glued on.), and you'll need to make sure you are able to put this under your stand (if that is where your sump is going.)
Some of the skimmers need a lot height in the stand. Once you have the skimmer picked out, you can design the sump to hold it