If you're interested in just displaying the mesh in the viewport, you could create a node descended from the MPxLocator class. This is the API class that lets you draw things with OpenGL in Maya. The footPrintNode devkit example included with Maya provides an example of writing a locator.
To turn the mesh into an actual polygonal object that can be rendered with Maya's renderers, you could write a DG node that calculates mesh data (using MFnMesh) that gets passed to a mesh object that can be shaded, etc. I think the shellNode devkit example demonstrates this.