You can download the latest version of boa_build via anonymous ftp from the ftp-server of the MPIfR Bonn:
ftp ftp.mpifr-bonn.mpg.de (anonymous) cd outgoing/schuller/boa
or using a web browser and enter as URL
ftp://ftp.mpifr-bonn.mpg.de/outgoing/schuller/boa/
If your computer is located behind a firewall remember to use a proxy in your browser settings, otherwise ftp may fail.
There are two archives, one is called allBoA.tgz, the other allBoaOff.tgz. The first one is smaller than 1MB and contains only the BoA-Software and a script which will download all additional needed software from the internet. The second one, allBoaOff.tgz, is huge, nearly 14MB, because it contains all needed software packages and does not require an internet connection. This second tar archive is the recommended one, because the versions of the software packages are consistent with the BoA-Software. If you would download all additional software packages from the internet, you may get newer version than the with BoA tested ones and may encounter problems.
If you want to see and reduce some example data then you should download the archive exFits.tgz as well and extract it in your installation directory.
For further details see also the README file (which is also included in the archives).