Looking around my home area, I found HS football bleachers showing up as buildings and an outdoor basketball court showing up as a building. Looking at the coloring of those features on Google maps, I can see how the mistakes might have been made. But still feels like it needs tuning.

To be fair, I checked my boyhood home in very rural Maine and it was correct for the size and shape of the multiple farm buildings.

Yeah some areas I looked at seemed fine (US, EU, Shangahi), but some the buildings are on top of the roads, and they look more like Perlin Noise than actual buildings. E.g main parts of Beijing.

OpenStreetMap and such have pretty good building footprints, sometimes enriched with building heights. Maybe that can be used for some correction

It's machine-learning generated "slop" honestly.

Looking at where I live and where I grew up the building heights are quite badly estimated.

- Some groups of houses around here that are more or less identically built but on sloped terrain are reported to have widly differing heights

- My neighbour building is reported to be half the height of this building (they're more or less equally high at 5 stories)

- A small office shack behind the neighbour building is reported to be taller than it (it's a single-story building, the neighbour building is 5 stories)

- The freestanding buildings on the farm where I grew up are like you said, badly combined, much of the estimation there seems to be dependent on shadows,etc.