Couple of things here.
First, determine what is meant by iconic, and then, what you mean by building.
My interpretation is - iconic means quickly relatable to a specific place. Buildings are generally thought of as places where people can congregate/live/work/be buried, for a period of time.
Taj Mahal - India
Great Pyramid - Egypt
Empire State Building - New York
Sydney Opera House - Australia
Each of these is used to symbolize a place. When you picture them, you think of buildings that represent a specific place.
However, keeping the same interpretation for iconic, and expanding the interpretation to include "structures' that are not inhabited by humans for a lengthy period of time, nor are they designed to.
Eiffel Tower - France
Golden Gate Bridge - San Francisco
Tower Bridge - London
Plenty of options here.....