ObserverLib Mod (1.18.2, 1.6.5) is a library modification that allows you to reliably observe block change in large areas with minimal performance impact. This mod lets you register an Observer – what it observes at the end is up for the implementation – to be used in a specific area. The Observer is informed of any changes that occur in the world within its area. These changes can be interpreted by the observer to determine if they invalidate or confirm their state. This could be used to determine if the structure has been completed.