If you had a paid off million+ dollar building in NYC?

[Gabrielle Plaia]

Hello! I am new to the forums after lurking for quite some time. My dad owns a building in NYC that was once his fathers when he came to America in the 1960s. It is in South Queens and is completely paid off, storefront is a nice restaurant and apartment is completely done upstairs. Dad is a very hard worker with two jobs. He has no idea about real estate investing and isn't quite aware of the great investment he has. If you were in his shoes, what would you do with that building, investment wise? Would you take a HELOC out from it to buy more properties? Looking for advice for him!