And how they would want to use their daily spell slots for their ~legacy.Is the building structurally sound? Of course there's also the question of how many level 9+ wizards there are running around.
For instance, a wizard might want their 5th-level slots for scrying or legend lore for information for that book they're writing (unless they want the slots for upcasting or item creation).
If they wanted to build structures, within the spell's parameters, they might simply construct parallel 100 ft walls (with occasional doorways and window gaps) and stick a 10 ft wide roof on top. Any lucky beneficiaries could work out their own internal and side partitionings.