Your building has a 3 phase 240v and you want to convert it to be 110v?

Best to get quotes from two or three licensed electricians for the installation of the necessary extra fuses, breakers, etc., testing and commissioning (= handing over to customer to use) of a 120V panel for as many circuits as you want. Though the question does not specifically ask about DIY ("Doing It Yourself"), if you are not a licensed electrical technician you should not even think of doing this kind of work as a DIY project because 3 phase 240V power supplies can kill you if you don't know exactly what you are doing. Depending on your local wiring codes and regulations, it may be illegal to attempt to do such work if you are an unlicensed person.