Bryan Chappell makes the comment in his book, Christ-Centered Preaching (p162), that while the structure of a sermon is not the most important question, it is one of the most common questions he is asked when teaching preaching.  Having given specific examples as the starting point for preachers, he then recognizes the great variety of options available to preachers.  The only constraint he gives are four criteria that allow different sermon shapes or structures to represent Scripture well and strike effectively at the human heart.  Every outline should be:

Faithful to the text – accurately representing the movement and meaning of the passage.

Obvious from the text – not imposed on the passage, but evident from it for the sake of those following you with the Bible on their laps.

Related to a Fallen Condition Focus – Chappell’s distinctive element of the FCF, which thereby allows connection between human need and divine grace in the gospel.

Moving toward a climax – which encompasses both the need for order and progression.