Your sketch 3D model is broken usually because the underlying sketch has errors—like non-closed loops, overlapping lines, or unconstrained geometry—that the software can’t use to make a valid solid.
Sketches need clean, fully defined shapes (closed, no duplicates) for tools like extrude or revolve to build watertight 3D volumes. Gaps or extra lines confuse the software, so it can’t form a solid.
Try your software’s "check sketch" feature to find issues (e.g., red-highlighted gaps) and fix them first—this resolves most broken model problems easily.