From experience... you won't save any money building a large aquarium yourself. I couldn't and I deal in glass. Unless you can get 3/8 or 1/2 inch plate for REALLY cheap, you might as well buy a new one (or even better, a used one). 100's and 125's end up in the classifieds all the time. Don't forget, if you build an aquarium, you need to build a stand too and a full aquarium weighs roughly 10 lbs/gallon.