|Barbarian by Cushart (http://cushart.deviantart.com)|
So I was thinking that it would be better to use a saving throw mechanic. A barbarian can rage on purpose, but needing a saving throw to see if it takes one or two rounds to build up. Or a barbarian might involuntarily lose it in situations with strong /stimulus/. I think the on-purpose rage save should be Charisma-based (against an easy DC), since it's part of his/her personality while the "hulk transformation" type rage should be Wisdom-based (against an easy DC), since the barbarian is trying to use some force of will to struggle with animalistic inner powers.
Then once the rage begins the player should roll for the basic duration of the rage, since the barbarian has is no longer fully rational and in control of her/his actions. I'm thinking that maybe a basic duration roll could be 1d6 rounds, with no adjustments. If the barbarian wants to terminate the rage before it runs its course then a Wisdom save (moderate DC) is needed. If the save is failed then the rage continues, but now the barbarian is Confused ("A confused creature is mentally befuddled and cannot act normally. A confused creature cannot tell the difference between ally and foe, treating all creatures as enemies.")
When a rage ends there should be physical and mental exhaustion. As per the current Pathfinder rules this will result in loss of all temporary HP gained due to the Constitution boost from the rage and becoming Fatigued. Optionally, if the rage lasts more rounds than the character's level, when the rage ends the barbarian must make a Fortitude saving throw or gain an additional condition (roll 1d6):
The additional disadvantageous conditions above make rage more of a two-edged sword. To balance the negatives, the benefits of rage could be increased a bit. That way raging has more of a "Go Big or Go Home" feel to it, which will probably appeal to barbarian fans.