This is an MCEdit filter that creates a circular wall using the current selection as a repeating wall section. It was suggested by Blueyoshi03 on YouTube.
This filter attempts to smooth out gaps. It uses a line drawing method to do this. The deeper you make your selection, the more stretched out the outside of the wall will be, but there will be as few gaps in the blocks as I can manage.
(The model above was made from the simple model below)
You can use structures instead of wall segments.
Here is the Villager Church re-worked as turrets and walls.
MCEdit Filters >