When you accept an order you’re agreeing to deliver it directly to the customer, so you should always deliver to the customer’s door. For customers who live in a block of flats, or other shared accommodation, that means delivering to the front door of their flat, not just to the building. Of course if the customer has asked you to do something different through order notes in the app, like meet them outside the building or leave the order at a reception desk, you should follow those instructions.