/lib/modules/3.16.0-28-generic/build is in linux-headers-3.16.0-28-generic 3.16.0-28.38~14.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-3.16.0-28-generic
/usr/src/linux-headers-3.16.0-28-generic