Making a hole in the middle of the plane

I’m pretty new to Unity. I’m experimenting with Unity and I would like to make a hole in a middle of the plane. Think as table with a hole (round, triangle, square shaped)in the middle where objects could fall in.
How could I achieve that?

For example something like this:

alt text

Unity is not meant for 3d modeling. Use Blender(free) or any other(3ds, maya, etc…) to model your holed plane, then import in Unity (fbx file).

You could modify the mesh at runtime, but that’s a hard thing to do. It would be easier to create the mesh with all holes in a 3D editor (like Blender or 3ds Max). If you need some holes to be “created” at runtime, make also some “plug” objects to block these holes: destroy or shift the plug to open a hole when needed.