When we decide if a building is Open or Close, we define if it will have walls. For example, in Open buildings, there are no walls, just a roof. These types of structures are usually used as a parking lot, for a sports field, etc.
On the other side, a Close building includes all its walls and is the most common. Its uses depend on the customer. Many projects have been for garages, warehouses, churches, and more.
In some rare cases, customers ask for impartial buildings, which means they decide to have walls and open spaces.