There are several different sets of binaries that can be built:

The core build, which produces a platform installer ISO and many additional binary packages and related files.
1. Version 5 and earlier requires a 32 bit Debian Squeeze machine, and takes about 6 hours and 150GB of disk space.
2. Version 6 and later requires a 64 bit Debian Jessie machine, and takes about 5 hours and 100GB of disk space.
The Debian guest tools
The CentOS guest tools and SyncXT server RPMs, which requires a CentOS 6 machine.
The Windows tools build, which requires a Windows machine/VM, the Microsoft Device Driver Kit (DDK), Visual Studio and more.

Building - Version 10 and later (and earlier)

Building - Version 5 and Earlier