I think this needs a way to save a building in parts like this to show the layout. Maybe with the ability place the entire building on the ground afterwords and if possible it's exace previous location if possible. Then you cold take a building in single player or another server and rebuild it.(as long as it doesn't stop others from building in it's place. It could also generalize parts so it's independent of material but provide basic snap positions for fundamental parts like foundations so you can have perfenct alignment to the original and rebuild it in the exact place as before if desired.

And by preexisting I don't mean one made of green parts. I mean a real building made of thatch/wood/stone/metal. Maybe it could savethe exact spot of the existing parts and replace them with green parts. Even green parts that are genralizations of wall/foundation/fencefoundation/etc that allow replacement of any type of material for initial building and replacement ofthe green part. (Without bypassing normal build order though.)

Maybe they will build this into the default game at some point that as your building is destroyed or removed you can see green outlines to stuff like this of the missing part and remove them as desired or leave them to rebuild etc.