Our approach for similar problem: draw zones without stamp and add them up in a schedule that we place on the layout along with the floor plan.
Ussually the required area calculation layouts are separate from the main floor plans and colour coded. By adding the same colour behind the cells of the schedule on the layout, it generally makes things quite understandable.
We use a python script that put the calculation of the area of all rooms in the apartment in a property in each room. Then, we use a label to retrieve that value on plan, linked to any room of the apartment.