Considering the middle bit first:
외관이 아름답고 다양한 디자인이 가능해 건물의 개성을 드러내기 쉽다
This means 'the appearance is beautiful, and many designs are possible, so the character of the building can easily come out'.
유리 건물이 점점 늘어나는 것은
means "speaking about the increase in glass buildings,"
means 'that's why'; 'that's the reason'
So the whole sentence:
유리 건물이 점점 늘어나는 것은 외관이 아름답고 다양한 디자인이 가능해 건물의 개성을 드러내기 쉽기 때문인데요
Means something like 'The increase in glass buildings is because they are beautiful, and it's possible to make a lot of different designs to allow the character of the building to come out".
It is a difficult sentence to me too. As you probably know, to break a sentence down, it helps to look for the conjunctions. 가능해 is a conjunction but it's hard to spot!