The script MATRIX generates a chroot environment made of fresh 2016.1 packages.
The it checks out the latest build scripts inside the chroot and executes the build script.
Build log is written into chrootdir/opt/ISOBUILD/build.log
This is the example string of build start

$ env PROJECT=soft/build_kde4_desktop_ee PROJECT_VERSION=rosa2016.1 TYPES="64u 32" DE=kde4 RELEASE=R11 ./MATRIX

PROJECT         - Name of the ABF project containing build scripts
PROJECT_VERSION - Git branch to checkout from the PROJECT
TYPES           - List of ISO image types to build ("32" or "64" for i586/x86_64 architecture, optional "u" suffix for UEFI support)
DE              - Desktop environment; defines the list of packages to use (like commonkde.lst or i586kde.lst for DE=kde)
RELEASE         - ISO product release version
REPO            - Repository to take packages from