Here is a plan I've used for my 75, 55 and 29. I'll be getting a 210 soon so I'll be using this also but with more vertical mid support and cross supports.
http://www.arbreptiles.com/cages/75g_stand/index.shtml
Credit to Clay D.
http://www.arbreptiles.com/cages/75g_stand/index.shtml
Credit to Clay D.