There's an observation deck on the roof with spectacular views.
There's a rooftop observation deck that boasts great views.
こんにちは。
様々な言い方ができると思いますが、例えば下記のような表現はいかがでしょうか:
・There's an observation deck on the roof with spectacular views.
・There's a rooftop observation deck that boasts great views.
展望台:observation deck
展望:view(s)
海の展望:ocean view(s)
夜景:night view
ぜひ参考にしてください。