Virtually all my tank building has been with plywood, and a standard 4x8 sheet makes one perfect 120-gallon tank (48 x 24 x 24 inches) with almost no waste. Nice, light, maneuverable pieces of wood and glass; I think it's a perfect first-tank project. It's about the smallest size where plywood starts to save you money over buying an all-glass tank, and even there it's a close call. The real savings start to show up around the 300-gallon mark.
You'd have to check into prices for glass or acrylic to determine at which point you save money by DIY. I susect that the ease of assembly aspect will be the same. But I'm sure that DIY-ers who use those materials will chime in with more info and opinions.