is there any way to use building planer with Monument Addons or will there come a support for it?

Not currently planned, because there is substantial client-side logic that would need to be implemented to accurately detect where to place entities, and also work to link the entities. Other plugins such as Uber Tool already have that set of functionality, so I'm not currently interested in reimplementing it all. I might reconsider in the future after the currently planned features are implemented.

In this direction, I am thinking about adding a command that you could use to register an entity that has been placed from outside Monument Addons, but that will probably require some additional work to get the building entities to link up correctly.

I am also planning to add support for pasting buildings in via Copy Paste, after some new APIs get added to that plugin.

nice :D looking forward to the the paste