If you want to try your hand at building your own sump, I'd recommend doing something small at first. Take your time and do a good job so the floors stay dry. If you opt to build something big, make sure you know what thickness of material you need to use before you start construction. Here's a simple sump based on the Model A that I used under my 29g reef years ago.
Do It Yourself sump using glass or acrylic baffles: Building your own sump using a glass tank isn't hard, nor does it have to be expensive.
Many hobbyists choose to use a glass aquarium, and then insert 1/4" (glass or acrylic) baffles, bonding these into place.
This is a very old page I compiled way back in 2004 to help organize a lengthy thread about a DIY calcium reactor. I'm reposting it because all of the included pictures, but I'm not offering up any other support or answers. This is simply documentation - learn from it, build your own, that's all up to you. :)
A video is coming in Spring 2015, but for the time being here are the guidelines:
I sell acrylic baffles cut to fit your aquarium via my shop: http://www.melevsreef.com/product/baffle-kit Once arrived, this is how to install them.
If you mimic the layout of the Model F on my site, you will be creating three zones. The layout is Skimmer zone on the left, Refugium zone on the right, Return zone in the middle.
You need to break out the Yellow Pages and look up "plastics"... call one up that seems near you, and ask if they sell AcryLite to the public. Most do. You want acrylic, not plexiglas - the stuff Home Depot sells. Plexiglas ages, turns yellow, gets brittle, and cracks. Acrylic is harder, and you can buy various thicknesses.