These are a few URLs that provide information about
how to build packages for Slackware Linux:

 Slackware Linux Essentials book
 -------------------------------

 http://www.slackware.com/book/index.php?source=x4132.html


 Linux packages
 --------------

 This web site has a great number of pre-built packages for
 Slackware.

 It also has a HOWTO about building packages:

 http://www.linuxpackages.net/howto/howto.php?page=package


 Slackbuilds.org
 ------------------

 This site has a huge repository of build scripts for Slackware.
 They are all 'SlackBuild' type -- eg the 'clean' builds
 (the preferred method -- i.e. these do not need slacktrack)

 http://www.slackbuilds.org

  
 Slackware's official build scripts
 ----------------------------------

 I also recommend that you look at the official Slackware build
 scripts that can be found on the FTP site in the 'source' 
 directory of the distribution 
 (e.g. slackware/slackware-9.1/source)