There are a lot of crazy huge tanks on mfk. Some cool heating options too. Using the homes water heater on a closed loop. A friend of mine just set up a pool in his basement, 4' deep 12' diameter and is using the water heater method. He is a MGK guy all the way
As for your tank build. I had planned on building one years ago and decided not to, but did ton of reasesrch. I would check out Garf.org they have a tank building feature that allows you to plug in your dimensions and will give you cut list and step by step on it. Consider 8x4x4. That way the base and back dont need to be cut just put in place Also Glasscaged.com for your viewing glass. Far cheaper than any were else.
Looking forward yo this build thread