It is customary for the architect to provide you with a detailed measurement statement. This shows how many square meters of tiles and running meters of skirting boards you will need for each room. These sizes are usually the strictly mathematical net sizes without considering cutting loss.
If you are going to do it yourself, calculate the required m² of tiles/room in metres in length x width. For the plinths, take the room's outline into account. Deduct the widths of doors, windows that go to the floor, and any cabinets