This is an automated build system based on qemu images (thanks to aurel32, Aurélien Jarno for the images) for Degeneratedlabs's Live Cds and for aircrack-ng unoficial packages currently keep at http://repo.degeneratedlabs.net
You usually don't need to, we do it for you, building weekly images that are shared via bittorrent (seed us! [0])
But, if you want to do it anyway, this is intended to be almost automated. You just download this repo, execute build_system_builder.sh (wich will prompt you to copypaste some stuff on the debian images) and wait. For custom builds you'd have to adjust the urls to point to your own repo (fork us!)
All the needed changes are made in the repo, not the build system (as it has to be)
Oh, and you'll need to setup... networking
The script uses a specific IP address for the bridge, it's easy enough to change it, But you can also just configure it as it is, copying the contents of doc/examples/networking to your /etc/network/interfaces file and restarting networking.