I modeled the building and added the additional part you wanted. I designed newly added parts of the building have the same features as the old parts. If you want revisions on some issues, I can do that too. I have taken various images from various angles. I prepared 2 animation videos and put them on youtube. Only one could be shared in the link sharing place, so I put the links here separately.
Video Animation-1
https://www.youtube.com/watch?v=G8hPf-xjzyY
Video Animation-2
https://www.youtube.com/watch?v=-gKwdYsOQC8