As many may be aware it is generally believed that Rand is the Destroyer, Mat is the Preserver and Perrin is the Builder.

We know that Rand will destroy. He already has. The Aiel beliefs have already been destroyed.

Mat will be the Preserver. He's working his way toward that as the son of battles.

Perrin on the other hand has not yet begun his task as the Builder. I've read many theories on the net regarding Perrin and his destiny and when it will begin. Most people seem to think he will become the Builder after Tarmon Gai'don.

In my experience with the Sci-Fi Fantasy genre I haven't come across many books where the story continues for long after the main climax.

Therefore I think Perrin will become the Builder much sooner. From Winter's Heart we get the impression that the 3 nations Rand has under his control are slipping through his fingers. Sooner or later Cairhien, Andor and Tear will rebel.

My thoughts are that if Andor rebels and elects someone other than Elayne as Queen they will discilpine the Two Rivers for flying the Red Eagle banner on Andorin soil. Elayne herself has said they cannot do this for too long without repercussions.

When this happens Perrin will decide that his course of action will be to unite the nations under the Dragon banner.

At this point he will discard the axe (or perhaps re-forge it) and take up the hammer.

Going out on a limb -

-Faile's mother and Davram Bashere will be killed defending Saldaea (Perrin will be the next ruler of Saldaea).
-She will come up with the idea of uniting the nations to try to prevent this sort of thing happening again.
-Berelain will support her and that's about the only issue they will agree on.
-The Two Rivers will be attacked by Andor and it's renegade Queen (not Elayne)
-In the remains of the Two Rivers Blacksmith forge Perrin will make his decision. Walking through the Blacksmith remains, remembering what it used to be like he will begin working the forge. He'll start hammering at his axe as a gesture of his frustration at having to carry something that couldn't do anything to protect his beloved home.
-At the end he will have decided to follow his wife's plans to rebuild Artur Hawkwing's empire. Then, when he looks down, his axe will have become a hammer.

As I said "out on a limb" but that's my vision of how Perrin will take the path of the Builder and carry the hammer instead of the axe.

Timeline? At the end of the eleventh book.