Assuming that the water will be rising the whole time until it reaches 12 feet, I would stay put. Unless I'm very close to higher ground, all transportation will quickly bog down very quickly long before the water gets very deep, and being stuck outside or in a vehicle in rising flood waters is far, far riskier than trying to ride it out in a tall enough building.

On the other hand, if we're talking something like a tsunami, lahar, dam break, or some other situation where the water will arrive all at once, I might consider making a run for it since the ground will be dry before that wall of water arrives.