I don't know of any site online, but I can recommend a book, "The Living Aquarium," by Hunnam, Milne, and Stebbing. It has a good-sized section on tank building, with a very helpful graph to help you select the correct glass thickness for the capacity.
The book is out of print, but you can probably pick one up reasonably on bookfinder.com or halfprice books (I think I got mine for $13.00).
Good luck!