Area Calculations

I'm currently working on the Decent homes standard in the UK, i'm drawing floor plans and elevations for council houses that need modernising. My client requires area of brickwork that needs repointing. Can any one help me with the area command?? When I try the subtract mode in ACAD it seems to add the area's. I'm trying to take away the windows area from the brickwork area. Does anyone know how to do it??
Many thanks
Steve

Command: area
Specify first corner point or [Object/Add/Subtract]: a Specify first corner point or [Object/Subtract]: o (ADD mode) Select objects: Area = 20000.0000, Perimeter = 600.0000 Total area = 20000.0000
(ADD mode) Select objects:
Specify first corner point or [Object/Subtract]: s
Specify first corner point or [Object/Add]: o
(SUBTRACT mode) Select objects: Area = 518.6613, Perimeter = 91.0965 Total area = 19481.3387
(SUBTRACT mode) Select objects:
Specify first corner point or [Object/Add]:
Command:
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Draw brick area outline as Polyline. Draw window outline and all other non-brick features as polyline. Use region command to declare each feature as a region. Subtract each feature region from the main brick wall region. Obtain properties for the resulting composite region which will include area of brickwork.
Phil