Create slab / wall based on archicad zone

Hello

we use archicad zones for early studies of our projects, often urban scale. i wish to create with grasshopper a slab on base level of every archicad zone, or a wall around the perimeter of these zones. as i am rather new to grashopper, i am not able to solve this problem: the resulting walls and slabs are in archicad all based on ground level, the project 0 level, no matter, which level the zones are based on. how can i extract the positioning (z coordinate) of the zone and create other archicad elements in the same position?
I tried several things, this is what worked, but as i said, in wrong position…

grafik

Thank you a lot

EDIT

i found the solution, as so often by accident. i was able to choose the parameter i want to access by right-click on the “deconstruct zone” , which is the “bottom surface”. before i had always accessed the default property “polygon”. now it works! I am happy!

Dierk