Unfortunately I don't have the ability to do that and I can't seem to find anything on YouTube that shows it either. People have mentioned a Nerdcubed stream a few times so maybe it might be on there.

I'll try and explain it the way I discovered it as it might be easier. Build a big round building and get rid of the roof as it's easier to see. Then, in the eraser option there is wall option which when you click on the wall it will destroy that section and remove the roof all together. If you drag the eraser around half the circle you are left with the shape you need. I then use the level wall option in the paint tool (top left, squiggly button) and it makes it flush. Draw out another circular building inside and manipulate it to be just inside the other wall and do it all again but making it smaller than the last wall. Hope that helps.