Is tempered glass necessary when building an aquarium?

I am looking to build an aquarium, I figured if I do it myself I could save lots of money. I am looking to build about a 200 gallon. At pet stores I have seen aquariums approx. this size and they would sell for around $900. I have called local glass companies and gotten quotes for 3/8 thick tempered glass and just the glass is about $1000 dollars.

Does anyone have suggestions or knowledge of building custom aquariums, where I could build my own for a fraction of the cost to buy a new one?