How to make round-ish buildings?

[Statistx]

Game puts fancy round buildings all over the islands, but trying to make one myself on the home island seems impossible. On foundations even more so than on the ground, but even on the ground i can't line them up with the round door, which i suppose should be for cases like that.
With the normal door it works on the ground, but not on foundations

[Raven]

Use the sketchbook to copy round foundations

[dtt.scanner]

You can use other pieces to line up the rounded ones, since they will snap, then delete the temporary pieces if they are not part of your design.