The tank overall is not worth building in my opinion. The cost involved in either getting the glass or plexiglass and then either fiberglass, epoxy or zavlar liquid rubber to coat the inside to make it watertight, make the tank for the size, go beyond what one could pick up secondhand.
Having spent months researching build a tank, the cost saving really only draws benefits beyond 250g+ Not to mention you MUST have a good grasp of woodworking and space to actually construct the tank.
Bare in mind, if you epoxy the tank you MUST MUST do this outdoors away from any ventilation inlet/outlets and wear a respirator mask, this stuff stinks and is extremely bad for your health. Also make sure that you can get the tank outside or indeed inside if you construct it in a garage.
For the money you will spend on this project, yes it gives a sense of achievement building it, but you could probably find a 125 - 180g (sometimes larger if you get lucky) tank secondhand.
If you do go ahead and build it, would be interested in following your progress, perhaps post a thread in the DIY section of the forum.
Best of luck