The building would have to be significantly taller than planned to give guests a view of he lagoon.
You would need to be 40m / 130ft to see lake top as seen here: http://forums.wdwmagic.com/threads/caribbean-beach-expansion.923827/page-34#post-7788231
So, according to the artist rendering, the resort is 9-11 stories... how high is that?
Of course, even if you could see lake-top from there... what would you see? A glowing ball and some intermittent flames? One can hardly make out the scenes on the globe from the lagoon's shore, let alone from an extra half-mile away.
I've watched Epcot fireworks from Pop and it was impressive enough seeing what popped up over the treetops.