Hi,
There is some lines visible inside the base polygon shape. According to the docs, it should appear only when angles between adjacent faces falls below a threshold.
Edit: Successfully used BABYLON.MeshBuilder.ExtrudePolygon(…) to build this shape as intended.
BABYLON.PolygonMeshBuilder(…) … build() or BABYLON.CreatePolygon(…) showed some glitch (i.e. missing faces).
Thanks.