(Text copied and pasted from a forum in Help, as I decided it would fit better here. Hopefully that's not a problem.)

I am confused as to whether the Sanctuary is meant to be unique or not.

On the one hand, it says that it is unique in the Craft & Construction tab, and you cannot build a second one after building a first.

On the other hand, upon clicking on its name in Buildings, it asks for the quantity which you wish to use. Even after asserting the use of only one Sanctuary, the next page also reminds you that only one Sanctuary is being used, and asks for quantity once again.

If the Sanctuary is meant to be unique, it shouldn't ask for quantity, or reference the quantity of 1 in any particular way. If the Sanctuary is not meant to be unique, it should allow multiples to be built.

Which is the case?

It's meant to be unique, but that one module of "choose how many you want to build' is on ever building.

It's not just that one module, it's also in the text of use. But the using text might be similarly the same for all regardless of uniqueness.