Spawn multiple volumes to make the walls spawn from, and define wall size based on the actor scale

Inside the subgraph, I borrow the public variable from the actor

Each mesh has a self-adapting scale based on the scale of the actor

Even with some variation, the walls fit in already!

Now adding the ceiling and the floors (my offsets based on meshes with pivot on the center-bottom, it may vary if pivots are somewhere else)

And we now have floors and the ceiling

With some offsets edges are added to each floor

Adding Windows

In order to make the frame fit, I assembled one in the scene and made it an actor

Modeling Mode is handy for editing the pivot

Some noise changes some walls into windows and spawns structures in them

Additional units(lights and vents)

The windows have random angles!

Sample the ceiling to add some meshes to the top

Making sure that they're away from the edge and each others

Another element made by adding offsets

...and that's pretty much it! (so far?)