If you have started to use Energy Evaluation in ArchiCAD 16 you will realize the importance of zones
If not, heres how important they are: VERY!
Energy Evaluation uses zones to see all the structures and openings which they touch
If the zone doesnt touch the slab, wall or roof they will not be part of the Structures list in the Energy Evaluation
There is only one way to place zones in plan view; using the Inner Edge zone placement:
The best bet for their height is to set them to go below the slab and above the roof like so:
Then use the same Connect command you would use when trimming walls to a roof
Or you can use Solid Element Operation to trim the zone to the slab using downwards extrusion