The "unofficial" two family

[Michael Jurewicz]

Hello all,

Is it acceptable/a good idea if you have the ability to turn your one family into an unofficial two family by finishing a floor with a small kitchen and bathroom? I used to rent a place years ago as a young man that was basically a studio apartment connected to someone's garage and paid them cash each month. I wasn't even thinking about real estate back then, but now when I think back, I wonder if they actually were "illegally (?)" renting their basement to me. I also wonder how difficult it is to do something like this, but I guess it depends on the construction of the house. Any thoughts about this??? 

Thanks!