Apparently someone bought one of the empty bris plots and planned a large vault there. Yay! Time for you hardcore crafters to help out I guess. But.. Having said that:
I'm guessing it's meant to be a community project. If that's the case I have a small quandary. Why a large vault instead of a small? Small uses literally 1/1000th of the resources and time/skill to create. Nobody uses connies outside of aug. and there is a T6 PB literally under that plot in my lair.
not that I would ever think to tell someone what to do with their plot (besides maybe give us dragons some Asian orange we can drop on these plots with the massive amounts of trees!). But if it's meant for the community to build (given the fact that it's the sole structure planned and there was a vault there before) then it needs to pass a community logic test.
Heck, you can build a T1 PB, T1 Connie AND a small vault all for less than the large vault AND in less space.
My two coppers.