most of the diy plans and advice i have seen recommend a 14" max height with 1/4" glass. not sure how big you could go on the footprint, but if you go bigger than 24" or so, i would recommend bracing the top. you could possibly eurobrace the top to avoid a center brace. personally, my opinion is option #6 if you are dead set on building your own tank. i built a 180 and it was probably the most difficult project i have ever done - and i ordered the glass already cut and cleaned on the edges.