Example of downloading a custom module with drush make
From http://drupalqa.net/375293/downloading-custom-module-with-drush-make
core = 7.x
api = 2
projects[cs_all][type] = "module"
projects[cs_all][subdir] = "contrib"
projects[cs_all][download][url] = "git@bitbucket.org:myrepo/cs_all.git"
projects[cs_all][download][type] = "git"
projects[cs_all][download][branch] = "master"