Art of illusion

1.  Select the polygon object.

Edit Mesh > Append to Polygon Tool

and click the edge.

2.  You click one by one the edge that you want to add the face. 

3.  The face is pushed out by operating the manipulator. 

When you select two or more faces and do Extrude,

if Edit Mesh > Keep Faces Together is on,

then faces are pushed out together as the above.

4. If Edit Mesh > Keep Faces Together is off,

then faces are individually pushed out as the above.