Extrusion creates black artifacts I am a complete beginner to Blender and to modeling, and am taking a tutorial for Absolute Beginners to create my first house.  No problems creating the point for the roof, but when I select the edges to try and extrude out the roof and create an overhang, the part I have extruded turns a scratchy grey color.  Later on when I try to add texture or color to the roof, the extended edges turn the same color as the face of the house, not the rest of the roof.  If anyone is able to translate my poor description and help, it would be much appreciated!  Thanks!!
You might have accidentally extruded twice earlier. If you press E and right click, it looks like nothing happened, but you actually extruded to the same place. Hope this helps somehow.