I am looking to build a sump filter for my tank. It is a 125 gallon reef. I
am curently using fluidized bed filters, but want to upgrade to a sump with
bio balls.

The problem I have is that I can't find a pre-made sump that will fit into
the opening of my cabinet. I have a 10" opening that I can fit a sump into.
What are the dimensions I would need to have a sufficent sump for
filtration? Also, is there a type of plexiglass that I need to avoid?

Any help will be appreciated.
Thanks,
Geoff