Hello. Thanks for mapping. 
You mapped quite a number incorrect.

About complex buildings. Especial the high rise (multi story) buildings and buildings which shows their side views  as well. Check this footage how to map these buildings 
https://www.youtube.com/watch?v=dsfUcslLtVc
https://drive.google.com/file/d/13RTwH7sChRWrG5bIjysF2ripBgh3F5l4/view?usp=sharing 

Lower buildings, showing their sidewalls as well, can be mapped on the same way by moving the mapped roofline to the groundplan.

Please square each rectangular building with the Q key.
Best regards and keep mapping