Infinity terrain: updating cardboard buildings (Mototronica pack)

I thought I had everything under control.

I made changes, rebuilding the vector designs for the laser cutter from scratch again, been really careful about dimensions and calculations.
And then I realized the MDF wood I had was 2mm thick, not 3mm as I thougth.
Lessons learned, first check the material, THEN start designing.

The first building I made was from 4mm MDF wood, and while it looked good, was a bit too thick, so I designed the new one thinking that 6mm total thickness (3mm for the inner shell that keeps the roof in place plus a 3mm outer structure) would look better.
If the MDF wood I had at home was 2mm, I could simply add an extra outer layer and gain the 6mm for the roof wall while also getting a deeper door and windows frame.

Win Win.

Except I forgot (again) to take into account the thickness of the material. As a reminder, I’m designing all of this in Illustrator with 2D vector drawings and doing all the 3D math mentally. It’s hard to remember all of that, I need to improve that part of the design process. Maybe I need some kind of CAD program, and a tutorial or two about how to use it.

It looks like this now:

The main thickness has improved and I’m really pleased about how it looks, but all the corners are wrong. I don’t want and can’t make the building bigger, as I’m limited by the size of the original cardboard building.
I could make the two inner layers smaller to compensate, but I can’t be bother to redisign the whole thing again.

So I have an idea, a compromise that might work just fine.

I’m going to bevel the corners.