Original: The largest and highest plateau in the world is the Tibetan Plateau, called the "roof of the world", which is still being formed by the collisions of the Indo-Australian and Eurasian tectonic plates. In all the Tibetan plateau covers an area of some 2.5 million square kilometres which is approximately 5000 m above sea level.
Simplified: The biggest, tallest plateau in the world is the Tibetan Plateau.