Thank you very much for your detailed feedback.
I primarily use the Japan GSI seamlessphoto Imagery as the most reliable source for accuracy, so I believe the building shapes are generally correct.
After that, I refer to Bing and Esri imagery to check for temporal changes, adding or deleting features as needed.
Regarding roof overhangs, since they vary by building, I traced the roof edges as a guideline. I understand your point about overestimating footprints, so I will pay more attention to this in future contributions.
Thank you again for your kind and constructive review.