Problems with BREW installing SIP:

$ brew install sip
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink include/sip.h
/usr/local/include is not writable.

You can try again using:
  brew link sip

$ brew link sip
Linking /usr/local/Cellar/sip/4.19.5... 
Error: Could not symlink include/sip.h
/usr/local/include is not writable.

Find /usr/local/ there is no path /usr/local/include
need to create this path and modify the permissions
Solution:

$ sudo mkdir /usr/local/include
$ sudo chown $(whoami):admin /usr/local/include

Success:

$ brew link sip
Linking /usr/local/Cellar/sip/4.19.5... 10 symlinks created