Certificate of Occupancy for commercial property in NYC

[Daniel Bryant]

A friend of ours inherited an occupied commercial property in Brooklyn, it is used for office suites and storage on all 4 levels. It is currently fully occupied.

When she inherited the property last year the estate attorney told her that there is no Certificate of occupancy in the property. She is in the process of getting one now through an architect/engineer but is worried about fines and fees that may or may not come into play from the Building department. 

What would you advise her to do? vacate all renters and get the certificate? Or start the process while the building is still occupied and ask for building department for an extension?

As always, thanks in advance for your help and happy new year!!