1/2 to 3/4 bath conversion (re-post in Renovation)

We are in contract for a 1 bedroom 1.5 bath apartment. One of the big selling points was the prospect of adding a small shower stall to the half bath to create a 3/4 bath that could be used by our son or guests. Such a conversion has already been done in an apartment in the same line with the same floorplan. We had a contractor stop by and take a look at the place. He was uncertain as to whether... [more]

We are in contract for a 1 bedroom 1.5 bath apartment. One of the big selling points was the prospect of adding a small shower stall to the half bath to create a 3/4 bath that could be used by our son or guests. Such a conversion has already been done in an apartment in the same line with the same floorplan. We had a contractor stop by and take a look at the place. He was uncertain as to whether the conversion could happen because the modifications might not meet code. The bathroom is approximately 4' x 5 ', with the sink and toilet currently located on the right hand wall. We envision a small custom stall and showerhead replacing the sink on the same wall as the toilet, and adding a tiny sink on the perpendicular wall. Kind of like this on a smaller scale, with a sliding or pocket door: https://s-media-cache-ak0.pinimg.com/236x/5b/2f/8f/5b2f8f4f2a87363e9aa8605ca340cde7--small-bathroom-layout-tiny-bathroom-design.jpg Assuming that the modifications might not meet code, as far as recommended sizing/layout, could the renovation be permitted because there is an existing fully compliant second bath elsewhere in the apartment? We are not so concerned with being fully compliant for our needs, given the presence of the existing full second bath; we are mainly concerned about not getting approved or being penalized for work that is not authorized by the building. Thanks for all and any input! [less]