Multiple Meshes/CollisionShapes in a GridMap item

Godot Version

4.3.stable

Question

Hi everyone,
I’m an absolute newbie trying to create a 3D grid based building system.

This is how I want the system to work:
The player can place “framework” blocks, which are hollow cubes consisting only of beams along their edges. Then, the player can attach walls to the sides of a framework block.

What I have so far:
With the help of a tutorial, I managed to create a basic Minecraft clone where you can add or remove blocks (and I was surprised how easy it was!). Then, I managed to add the functionality to slap walls onto the faces of the blocks.

But now I am stuck and need some advice on how to make a hollow block with solid edges.
When trying to make the framework block out of multiple MeshInstance3Ds, each beam appears as a separate item in the MeshLibrary for the GridMap.

After a quick research I found a post here where someone asked if an item for a GridMap can consist of multiple meshes, and the answer was “no”. But I couldn’t find out how to approach it instead in my case.

That’s why I need some general guidance on how I could approach this.
What kind of nodes do I have to use? What kind of collision do I need? Can I get this to work with just nodes, or should I use a “pre-made” mesh of the framework block and could I use that for collision? Or something like using a placeholder block and then placing the actual framework block in a script?

I can probably figure out how to use things, I just currently have no idea what things I have to use.

Thanks in advance for any advice or pointing me into the right direction!