Start with the diameter, not the radius
A block circle is a raster approximation: square blocks describe a curved edge. Choose an odd diameter when you want one exact center block, or an even diameter when the center should be a two-by-two gap. Enter that diameter in the generator and keep the center guides visible.
Mark the axes first
Place temporary blocks at the top, bottom, left, and right extremes. Then mark both center lines. These anchors keep the build aligned even when terrain hides part of the outline.
Build one quadrant
Read the row plan as short runs. Complete the upper-right quadrant, mirror it across the vertical center, then repeat below. Do not try to judge the curve by eye at ground level; count each straight run.
Check symmetry before filling
View the outline from above or from a scaffold. Every run on one side should have a matching run on the opposite side. Correcting a one-block drift now is faster than fixing a completed wall.
Raise or fill the structure
For a tower, repeat the verified footprint upward. For a floor, switch the generator to Filled and place each row from the center outward. The material estimate shows full stacks plus loose blocks so you can prepare inventory slots.
Keep progress locally
Turn on build progress and click cells as blocks are placed. Progress is saved only in this browser and isolated by the exact dimensions and settings in the share URL.