Legalizing rental property on Long Island

[Justin Simoes]

I am currently thinking about buying a house in Nassau County NY. It’s an expanded cape and the upstairs has 2 identical apartments with seperate utilities from the main floor. I would live in the house while renting upstairs for the time being. My question is when moving on to the next house. How expensive will the process be to make the house 100% legit to rent the 3 total units when I leave? I don’t believe much if anything needs to be done to bring apartments to code.