Map "rooms" to paint features on the base background

This could function like drawing a room except it would not erase the background and replace it. It would instead add the "feature" to the background. Examples are:
Stone monoliths, circles etc.
Spider webs.
Mushroom forest.
Ruins - AI generated wall fragments, pathways etc.
All would be AI generated and would behave like a drawn room with delete, resize and redraw etc.
I am sure there are many other features that could be painted to the backgrounds.