Conversion of a dumbwaiter to usable space in a NYC apartment is a popular idea but must be done according to NYC code. A dumbwaiter is a chimney, and as such must be sealed up by a fire resistant assembly. Use of plywood creates a fire hazard and is illegal.
Dumbwaiters may also be structural, or bearing, elements, and their removal may cause problems with the upstairs, or downstairs neighbors. Floors may sag. Walls may crack. If you plan to do this work make sure that you have the blessing, in writing, from the powers that be. Otherwise you may be liable for making repairs elsewhere.
Most prudent buildings require the shareholder to pay for an engineer’s report (typically $500 – $1000), and where I may be needed to make some probes in the walls in order to see what’s a bearing member. Keep these documents safe because structural problems may not show up for a year or so, and then everyone’s trying scrambling trying to figure out who is liable for the damages.
Dumbwaiter fire https://newyork.cbslocal.com/2018/01/08/riverside-drive-fire-upper-manhattan/
NYC Building code http://www.nyc.gov/html/dob/downloads/bldgs_code/bc27s18.pdf
Technical drawings and correspondance with city officials