Hi Atulsuri,
Autodesk Quantity Takeoff has been discontinued since 2014. Quantity Takeoffs have been incorporated into Navisworks, and works just as well. I cannot seem to find download links anymore through either the subscription center, nor on the website for earlier versions of QTO. You can have a look at the following link for more information: Future of Quantity Takeoff.
Navisworks is a brilliant program to start off with, and the QTO features makes it even more valuable, especially in your line of work
http://revitrecess.blogspot.com/
