The AltOS source tree has a fairly long list of build dependencies, because it builds firmware for at least 4 different processor cores, ground station software in Java, various utilities in C, etc. By far the easiest way to build from source is to start with a Debian 'unstable' installation and take advantage of Debian tools and processes. From this platform, it is possible to build installable packages not only for Debian, but also for Windows, Mac OS X, and generic Linux.
Install Debian, then type 'apt-get build-dep altos' and all of the required build dependencies should be automatically installed.
The notes we use to do a complete build for release are in the file Releasing in the root of the source tree. Not all of those details are necessary unless you're trying to do an official release, but all the info necessary to rebuild from source is captured there.
If you really want to try and build our source tree on a development platform other than Debian, feel free... just don't expect us to help! It's hard enough keeping everything working on one development platform...