sump question

[Jaws]

I was just wondering, if you're going to be building your own sump out of acrylic, is there a better design than basically a normal fish tank with baffles? What's the advantage in building your own sump out of acrylic instead of just buying a 70G tank (which is about what I need) and putting glass baffles in it? Is it better to cut holes in the side of the sump for your overflow to flow in to rather than just have the water falling into the tank?