build\envsetup.sh file not found while building android marshmallow image

Question

I am building android image as given on the website

https://source.android.com/source/downloading.html

then it says to source build/envsetup.sh

on the next page https://source.android.com/source/building.html

but i cannot find build directory and envsetup.sh

I am using ubuntu 14.04

size of .repo directory is 18 GB (have i downloaded all)

What might be the issue ?