Builder Base walls upgrade as connected segments
The Builder Base handles walls differently from your Home Village. Instead of upgrading individual pieces, Builder Base walls upgrade as connected segments — a whole run of wall raised in one action — and they cap at level 9, paid for with Builder Gold. That segment mechanic makes the grind shorter than the Home Village's 325-piece marathon, but Builder Gold is scarcer, so the loot pressure is just as real. The table above shows the level bands by Builder Hall.