The Istanbul Sapphire tower is the tallest building in Turkey (as at 2012) and I wanted to be on the roof top before the golden light hour. The journey from the old town of Istanbul to the Levent area (business district) is quite a journey requiring a tram, funicular and metro. Give yourself an hour from getting on the tram in the old town area to standing on the roof top.
There are two viewing levels, the first is where the roof top bar/restaurants are and is surrounded by floor to “ceiling” glass walls. They reflect the interior and are dirty. The second level is the actual roof top with an approx 4 foot high wall around the edge and no windows, giving you a clear line of sight. You can take a tripod too.