There is a script under the product builder called build-site.sh that will assemble an update site from the specified build, and upload it. (Note: you will need to have ssh.publishing enabled as well as a configured a ssh private key that is authenticated with download.jboss.org)

Here is the usage for the script:

$ ./build-site.sh
Usage:

  ./build-site.sh [site-type] [version] (build-type)
    site-type:  The update site type to build. [development|stable]
    version:    The version to build this update site from.
    build-type: The type of build this update site is for. [release|integration|nightly] (optional: default 'release')

The files that are used for generating the update site can be found under builders/product/updateSite