Outdoor HB UTCI Comfort map for non-watertight model

Hi everyone,
I’m fairly new to Ladybug, but experienced with CFD, so I know my way around models and physics. I have inherited a workflow which is using the LB UTCI, but I’ve picked up on this forum that the HB UTCI map might be better. So I would like to “convert” the existing workflow to an HB one.

In essence I have a large building structure where I’m not at all interested in what’s inside, only the outdoor parts. My question to start with is really how a room is defined for this purpose, especially when there is no watertight version of this building. I have a model, but it would be tedious to recreate it as watertight. (I used a mesh version of the geometry in the LB workflow.) Is there a simple way forward here, as I assume Rooms must be created?

Also, from the CFD I already have the planes/meshes I would like to perform the UTCI analysis on.