I visited the excellent Sky Garden on the 35th floor of 20 Fenchurch Street, London aka The Walkie Talkie building. The views up here are excellent, although it could be difficult to take clear shots through the glass. Here’s three tips that may help:
Get yourself a circular polarising filter. It’s good for darkening skies, but it also helps dial down reflections on glass (and glare on water). It didn’t work that well for me, so I put my lens right up against the glass shot in Manual Mode and focussed at infinity. If you’re concerned about your lens touching the glass surface, get yourself a rubber lens hood.