I love the subtle shades of brown you are using to colour the rooftops

I think you have the right general idea about the shadows, but they are complicated things, so someone else may say differently.

One thing I see from the shadow you have drawn above is that you are missing the bit cast at the end of the building, which will still exist even if it doesn't hit the other building, because the gap between the buildings is not aligned with the light ray, and light will not fall into it to cancel out the shade at that end of the building.

Like this:

Click image for larger version.  Name: shadow example copie.jpg  Views: 27  Size: 91.3 KB  ID: 92595

I know that extra bit I've put in would mostly be part of the other building's shadow, but there would be no gap between the shadows like there is between the buildings.