List Management / Solid Union in Lists

Hi dynamo folks,

I’m struggling with solids and lists, respectively.

First, what I’d like to achieve: The target is to create cropped floor plan views from rooms based on a specific room parameter (number of apartment), with some offset to show surrounding walls. The rooms can be on different levels, and different apartments can be on the same floor.

What works so far: I can create room outlines, offset to theoutside, create solids and intersect them.
What does not work: I cannot just union solids of the same “level” in my solid lists, union just joins all solids, leaving only one solid per level.

Does anybody have an idea how to solve this?

There is a node in Chynamo called Element.FilterByLevel that could help