Thanks for your response.
The Bing imagery is not always that clear. Switch to the ESRI world imagery for a more clearer view. Your mappings often went wrong due to the vague imagery.  Also, On this task, the high-rise buildings are incorrect mapped.
You can see both one or more side walls and the roof. The Imagery is taken under a certain angle, so you can see more than just the roof.
Often all visible walls and roofs are mapped as 1 building.
The correct way is to map the roofline and move the whole object on their footprint.
See this video.
https://drive.google.com/file/d/1V5-bADsYiffCD9bo6l64YOdTvmKqMGry/view?usp=share_link
Best regards