How did you align them in the first case? By calculating their Y coordinate to be half the thickness difference? Or is there a way to align them in the UI?

I'm trying out Sweet Home 3D but I couldn't figure out how to draw a wall that is not rectangular in shape, like this:

https://i.imgur.com/pHFZoWg.png

At first I thought I could just draw two segments with different thicknesses, but of course then I get this:

https://i.imgur.com/p9q7uHs.png ...