Hi,
great news. Renderings for the new United Nations tower are up.
The tower is designed by Fumihiko Maki and FXFOWLE. Maki also designed 4 WTC which is currently under construction.

image from:
http://ny.curbed.com/archives/2013/09/18...tions_waterfront_skyscraper_revealed.php
Building will be 546 ft tall, or 166m and will be located on 1st avenue and 41st/42nd street next to the UN building. The building will have 850,000 sq ft of office space and house 2700 UN employees.
Construction begin 2015 and last 3 years. However on Maki's website it says 2016.
This picture is from Maki's website
here
This information, including the pictures, are all available at ny.curbed.com in the article "Unexciting United Nations Waterfront Skyscraper Revealed" by Hana Alberts Sept. 18th, 2013
More info at:
http://ny.curbed.com/archives/2013/09/18...tions_waterfront_skyscraper_revealed.php
The responsible Community board, Community Board 6, which is responsible for approving this project will hold a meeting about this building on Sept. 24 at 6 p.m., in the Farkas auditorium of NYU Langone Medical Center, located at 550 First Ave.