Simplify the following text for a Grade 6 native English-speaking person.
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 .