Please find the build procedure and other supporting documents at 

http://www.wirelessleiden.nl/projects/nodefactory/wiki/NanoBSD

= Directory layout =
README.txt	=	currently reading
cfg-files	=	extension for auto populate /cfg slice in image
cfg/kernel.*	=	kernel config files, different hosts
cfg/nanobsd.*	=	nanobsd config files
files		=	extension for auto populate / slice in image
pkg		=	Packages to be installed
tools		=	Helper scripts for use after image
patches		=	Patches to stock FreeBSD, mostly backports from -CURRENT