AbsLibre is the Parabola equivalent to the "Arch Build System". It is a git repository containing all of the build recipes for all packages in the Parabola pacman repositories.
The AbsLibre directory structure has a top-level directory corresponding to each pacman package repo, as defined in /etc/pacman.conf, e.g. [libre], [pcr]. Beneath each repo directory, are directories for each package in the the system, e.g. libre/iceweasel, pcr/h-client. In each package directory, there exists a PKGBUILD build recipe for that package, and often some auxiliary files used during the build process. The build process is described in the Usage section of the makepkg wiki article.
To build a single package, it is sufficient to acquire only the files in that one package directory. These can be downloaded manually with a web browser by visiting the following URL: https://git.parabola.nu/abslibre.git/tree/, and browsing to the package directory in which you are interested. If you plan to build packages often, you can use the git program to download them all at once.
To download the entire AbsLibre git repo:
$ git clone https://git.parabola.nu/abslibre.git