Standard 20-pound liquefied petroleum gas (LPG) containers may not be used or stored on balconies, roof decks, roofs, yards or courtyards of apartment buildings or or other residential buildings that qualify as a multiple dwelling (three or more residential units) in NYC.
The good news is that you are allowed to use a propane tank smaller than 16.4 ounces for a short period of time on a roof. However, you are not allowed to store the propane canister on the roof itself for any period of time.
The NYC Fire Code is slightly less strict on the use of propane barbecues when it comes to one- or two-family homes. You are allowed to use a propane barbecue grill with no more than two 20-pound LPG propane tanks.