I built a 60x60 base that was over 100 blocks tall from basement to top floor ceiling. It had 3 floors and a split level.
I suck at automation, and my plant and animal farms were outside. I still felt like I didn't have enough room.
Anything small that I build always seems cramped once I start adding machines. My "basic" structures usually run around 30ish by 19ish. If I build in a cave I spend most of my time making it not look like a cave inside. This stops me from ever building tech stuff. I hate caves, they're dirty lol.
TL;DR I build randomly and I like creme brulee
I heard you wanted some space...
Bottom circle is 128 diameter. Top one is 30 something I think. You can also see where I'm clearing down to bedrock.
And yes that is a dynmap screenshot because I can't possibly get the whole thing in one SS.