Heading to NYC - question about photographing city skyline

Actually just a simple question on what building rooftop with public access should I go to in order to get a good city skyline view for a photo?  

It's difficult to see the forest through all the trees, so you need to be outside the forest in order to see it. For a good city skyline photo, you should be finding some place outside the city to take a photo of the city skyline. The top of the Empire State Building observation platform will let you take photos looking downward at the city in all directions from there, but you won't get a skyline shot from there. NYC is a "very big place".

If you have a good telephoto lens and tripod, there is Bear Mountain Park with a look-out tower about 40 miles North of Manhattan on the West side of the Hudson River. On a map, look for the Bear Mountain Bridge across the Hudson (similar design to George Washington Bridge) (or look for Hwy 6 on map below). The tower is on the mountain just Southwest of the bridge (Bear Mountain) with a winding roadway up the mountain and a good viewpoint of Manhattan, even from the parking lot at the top, which is about 1,100 ft above the river. The Perkins Memorial Tower at the top of the mountain is a stone and concrete structure about 150' tall for an even better viewpoint, but the windows may make it difficult for clear photos through them. 

For a closer view of Manhattan from outside Manhattan, the New Jersey side of the Hudson and Palisades area along the Hudson River directly across the Hudson River offer good viewpoints of Manhattan. You will be about 1 mile away from Manhattan at this point. The Palisades (high vertical cliffs) are several hundred feet above the Hudson River, and there are small parks with viewpoints of Manhattan from there, but I'm not familiar with any good specific points to get you the better viewpoints there.

For a good topographic trail and road map of Bear Mountain Park see this link - 

parks.ny.gov/documents/parks/BearMountainTrailMap.pdf

It's been 41 years since I lived in the area of Bear Mountain, and 9 years since I've been to NY City.

Charley