I have another idea that might be useful. But I need to describe some context first:
To tackle the problem that sometimes part of a building’s walls can have a different colour, material etc. than the rest, I’ve thought about proposing a building:wall=yes tag. It would allow you to draw a way on a part of the building outline and add tags like building:colour etc. to it.
It’s loosely based on an idea I discussed with Kendzi in the past. The idea was well received in the German community. I’ve also created a quick test how this could be implemented in OSM2World, perhaps this clarifies what I’m talking about:
So what does that have to do with leaning towers? I was thinking that, maybe, we could add angles to the building wall ways. This would allow different leanings per wall, plus buildings that get wider or narrower towards the top.