Flipping a loft into a separate unit (zoning question)

[Alex Maas]

I am contemplating purchasing a duplex that currently has a massive loft on the third floor with a full bathroom in it. The loft has a separate door in the stairway so it is not connected to the upper unit (although the current tenants in the upper are the ones who have access to this loft). So my question is, if I buy this duplex and want to turn this huge loft into a studio as a third unit, what am I going to need to do as far as zoning? I will need to add a fire escape, hopefully a ladder down to the balcony will do. Are there any other complications that I might face? Thanks in advance.