Hi,
In my experience a simple example is straight forward, you can use nodes from Genius Loci to get you going.
Like all these things, the complexity comes from all the edge cases, and there are a lot!
- External wall dimensions should ignore intersecting walls
- Internal walls should include them
- We need to only work with walls intersecting the view cut plane
- Some walls aren’t 90 degrees
- Sometimes people put plan regions on
- Sometimes people use compound walls
- Sometimes wall joins give extra lines (you can temporarily change the join to mitre)
And many more, I’m sure 
Some stuff here
Hope that helps,
Mark