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There are two ways I can see this going. I’d probably start with this option:
1. Locate rooms and usage types (tenant or non-tenant).
2. Identify bounding wall types and widths.
3. Extend room boundaries by conditional offset (full width or half width).
4. Assign area value.
But you could also try this:
1. Identify wall types and conditions.
2. Determine offset based on requirements.
3. "Enclose" areas (there will likely be gaps between wall connections).
4. Match enclosure with room and assign area value.