You're welcome, and thank you for your response and explanation of your workflow. I have taken a look at the Japan GSI seamlessphoto layer in this area and think that you made a good decision to use it to obtain footprint shapes; the way the scenes are lit make the roofs more visible than in other sources. Beware that this layer seems to be compriesed of many secenes captured at different angles so buildings not too far from one another may have visible walls on different sides.

Do you know the claimed positional accuracy of that layer? you can check the meta data of a lot of the default soueces here https://livingatlas.arcgis.com/wayback/#active=21485&mapCenter=12.05732%2C25.09106%2C1&mode=explore

I agree that the building shapes are generally correct, just that some could have been mapped slightly smaller and moved to the base of the building. 

When mapping with imagery captured at an angle, please position features where they are at ground level. You can map the outline of the roof and then reposition the building to the base of the walls. I recommend you watch this [video about mapping dense urban areas](https://youtu.be/JAPiGntG6fs) and read this [written guide](https://wiki.openstreetmap.org/wiki/Roof_modelling#Typical_errors_in_the_interpretation_of_roof_geometry_from_aerial_images). Most buildings here are not as tall as those in the video but their walls are visible.

It's true that we cannot always know the exact ammount of roof
overhang. In situations like this I think there is a range of accurate building sizes. I tend to aim for ~ 95% of the size of a pitched roof in general when I cannot see a building's walls directly. This allows me to map quite quickly as I don't have to be pixel perfect and allows enough room for other features.

I also like to use multiple imagery layers to aid my interpretation. You may already know these, but I wanted to share a few tips; 
1. Lowering the opacity of layer [2] to 50% while aligning it with layer [1] can aid with the process. 
2. You can use the shortcut alt+number to toggle the visibility of layers in JOSM.
3. when working with multiple layers via a tasking manager employ a standard message with the sources you use used and paste that into your task comment; many conrtibutors do not use OSMCha, so will likely not know that you used other sources. If you like you can also post your workflow in a project's comments section if you think it'll help others.

You use the buildingstools and extrude working modes, right?

In future I will be more likely to check the sources attributed to changesets, and the JOSM default imagery layers which are only available in certain areas to gain better understanding of the imagery context.

Thank you for your contribution!