The Shuchan Aruch (YD 286:22) says that if you rent or borrow an apartment you are obligated to put on a Mezuza after 30 days if it is located in Chutz LaAretz. If the apartment is in Eretz Yisroel you are obligated to put up a mezuzah immediately. Your office, says the Shevet HeKehosi (4:263), is loaned to you and therefore in principal you are required to put up a mezuzah on the door.However, he adds, you are not the sole interest in your office and the owner of the business is a “Shutaf” in it as well. Therefore if it is a Jewish owned office you need to put up a mezuzah. However if the owner is not Jewish you are patur since “Shutfus” of a Goy exempts you from the obligation of putting up a Mezuza according to the Rema (YD 286:1) and most poskim (although some argue).