[bambax]

Here's a photo of the church tower in question:

https://img.over-blog-kiwi.com/1/40/25/08/20170227/ob_76f390...

You can see that the square base is connected to the octagonal tower using alternating trapezoids and triangles; FreeCAD doesn't seem capable of doing that using the GUI (but I'm no expert and would love to be proved wrong).

[alright2565]

This is what the other person was trying to describe: https://imgur.com/a/J9lQBNK

I chose 1mm for my corner chamfer on the base, but you could make it any dimension including something imperceptible.

[bambax]

Aah thank you!!!

Yes that would have worked, I will try that next time. The last image is more or less what the Python code produced, but being able to do it in the GUI would be nice.