You need to go to Ministry and apply for CR and after getting the CR you must go to Baladia with Building licence without which they cannot entertain you. After Baladia accepts the building to open a Restaurant you have to go through the process of inspection by Environment and Fire Department too, When you get clearance from the three departments you will be able to open the restaurant. There are so many agencies in Doha who can help you getting done all the process by charging a fee.