Joining Vertices/Making Faces

Occasionally when I join my vertices or make new faces one of the faces on my model will turn completely black. If anyone can tell me why this is happening it would be greatly appreciated.

most probably its just a “normals” ( wrong orientation) problem!
Select the “bad” face, press W key and choose “Flip normals” in the menu…it should be OK now, I hope?!

It also depends on the point order that you are selecting verticies in, or if you pick a vertex somewhere other than the local area, and it tries to place a face that way.

That’s exactly what the problem was. Thanks for the help.