Bootstrapping a Gentoo Prefix system is done using bootstrap-prefix.sh. Automated bootstraps can be run using the noninteractive feature of the script. On this site results of automatic bootstrapping for a number of platforms can be found.
The dobootstrap script is a wrapper around bootstrap-prefix that sanitises the environment somewhat and bootstraps in a predefined directory bootstrap<bitwidth>-<YYYYMMDD>. This script can be downloaded from here. Note that the script needs adjusting, because it sets GENTOO_MIRRORS and holds a path pointer to a locally available version of bootstrap-prefix.sh. Internal clients retrieving the file over NFS will be detected and automatically use a local version of the bootstrap script and publish their results.
The results of a bootstrap for internal clients are partly copied here for inspection. This is most importantly the stage logs and the distfiles used. The final prefix is not copied.
Find the results here.