Extension to automatically calculate area of multiple surfaces?

This is a long shot, but is there an extension that will auto-calculate the area of specified surfaces?

I want a quick way to calculate something like “Area of Surface 1 + Area of Surface 2 - Area of Surface 3”

I am designing a house and I need to stay below a specified number of square meters, and as I change the design I need to keep doing those calculations manually. An automated way of doing this would be very helpful.

If the surfaces are in the same drawing context you can just select them all at once and read the total area in Entity Info.