To build the system (experts only):

Requirements:

- Your build environment must be FreeBSD 9.2-RELEASE (building on
  FreeBSD 10 or 11 is not supported at this time).

- an amd64 capable processor.  8GB of memory, or an equal/greater amount
  of swap space, is also required

- You will need the following ports/packages when compiling anything
  FreeNAS-related:
  - devel/git
  - sysutils/cdrtools
  - archivers/pxz
  - lang/python (2.7 or later, with THREADS support)
  (and all the dependencies that these ports/pkgs install, of course)

Building the System Quickstart Flow:

- Checking out the code from git:

% cd /path/to/your-build-filesystem
% git clone git://github.com/freenas/freenas.git
% cd freenas

- Build it

% make git-external
% make checkout
% make release

This will also fetch TrueOS and ports for the build from github.

The End Result:

If your build completes successfully, you'll have both 32 and 64 bit
release products in the release_stage directory.  You will also have
a tarball in your build directory containing the entire release for
easy transport.