I think I have my 2 dream tanks:
720 gal, large sump, all nicely plumbed, built into wall FLUSH and SMOOTH looking,access room behind it with sink and dsiposal and powerful vent fan to remove moisture, lighting and fans and moolight all on timers, skylight over the top for natural light during most of the day, natural fine grain gravel and huge driftwood centerpieces collected from local river with a sweet collection of large predators, both common and unusual.
200 gal cube (3x3x3) planted tank mounted in wall as penisula, all built in and flush, natural sklight lighting it, in addition to moonlight and PC on timers. Nice collected driftwood. All low tech. Collection of small fish, some very common (platys, mollys, etc) and some very unusual (Vietnamese FW blenny, Candystripe goby, trumpet nose mormyrid)... etc etc.... These tanks are next to each other.
If it sounds like I am bragging... well I am... I am very happy with my tanks!! Sorry. Been waiting 30 years for this setup!
BUT, honestly, my DREAM tank that is Possibly attainable for me would be slightly larger... perhaps a 20'x8'x4ft tall tank. Still builet into a living room (not hidden in a basement). Probably will not ever happen, but maybe someday.....
I would post pics but I don't like the MFK watermark on my posted photos. Sorry.