Don't underestimate the time, money, patience, and precision required to build a large tank. If you want a standard size, remember that it will actually cost more for you to build it than buy it.
Do you have a very large, completely level work surface? Tools? Can you make near perfect cuts with consistency? Have you ever worked with glass, acrylic, fiberglass, or epoxy before? I don't want to be a stick in the mud, but I've done a lot of research on this (including spending a little time in 2 different acrylic aquarium manufacturing shops, 1/2"+ acrylic joints are an art...) and concluded that the DIY approach just isn't worth it for the vast majority of situations.
I considered the time(!) and money I have invested in this hobby and was able to justify spending the extra bucks to have my 300 built by a pro. I'd suggest the same to most people for any tank < 10'x6' (max sheet size before going custom) footprint.
If money is the big issue, you might consider compromising with an indoor pond. They are a great way to get a lot of water volume with relatively little money. They are also much easier to build.
Good luck and let us know what you choose!

Do you have a very large, completely level work surface? Tools? Can you make near perfect cuts with consistency? Have you ever worked with glass, acrylic, fiberglass, or epoxy before? I don't want to be a stick in the mud, but I've done a lot of research on this (including spending a little time in 2 different acrylic aquarium manufacturing shops, 1/2"+ acrylic joints are an art...) and concluded that the DIY approach just isn't worth it for the vast majority of situations.
I considered the time(!) and money I have invested in this hobby and was able to justify spending the extra bucks to have my 300 built by a pro. I'd suggest the same to most people for any tank < 10'x6' (max sheet size before going custom) footprint.
If money is the big issue, you might consider compromising with an indoor pond. They are a great way to get a lot of water volume with relatively little money. They are also much easier to build.
Good luck and let us know what you choose!
