Complex sentence: Upon completion, it will become the tallest building in Europe, standing at with 70 floors, and 5 levels underground, but the top of the tower has been modified during construction and the superior technical floors are expected to culminate higher (340 m?).
Split into simpler sentences: Upon completion, it will become the tallest building in Europe, standing at with 70 floors, and 5 levels underground. But the top of the tower has been modified during construction and the superior technical floors are expected to culminate higher (340 m?).