The instructions in my previous post about building an image for the Beagelbone Black rely on a pre-packaged root filesystem. Here are a few simple steps on how I build my own rootfs.
Run debootstrap, need to be root for all of these tasks.
Now perform any customizations needed. I.e. the rootfs changes in the previous post instructions could be performed now.
Copy the qemu binary to the chroot future chroot.
Now chroot to the new install and run second stage debootstrap. Also create a place to mount uboot and create an archive of the file system.
Now we have a complete proper root filesystem. The tar archive is at /tmp/rootfs/archive.tar.