Keep an eye on 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 

Don't forget to square each rectangular building as well.
Best regards and keep mapping
