Create Debian GNU/Linux instance-store-backed AMIs with minimum pain. Built Wheezy images well tested. Actual building (execution of this script) also tested on a Wheezy instance.

build_ami

#!/bin/bash

###### Description
#
# This script creates an instance-backed instance.
#
# Please excuse the lack of error checking for now.


###### Variables
#
# Useful to declare up front for use in other variables:
declare -r build_date="$(date --utc +%Y%m%d%H%M)"

# Change these as required:
declare -r ami_description="Debian 7 (Wheezy) built ${build_date}"
declare -r ami_codename="wheezy"
declare -r ami_suffix="${build_date}"
declare -r ami_arch="amd64"
declare -ri ami_size_in_gb=8
declare -r build_charmap="UTF-8"
declare -r build_locale="en_AU"
declare -r build_timezone="Australia/Melbourne"
declare -r build_filesystem="ext4"


###### Code
# Nothing beyond this point should require touching.
#

declare var
declare repo
declare repo_dirname
declare -r build_deps="ca-certificates euca2ools git"

if [ ${UID} -ne 0 ]
then
    echo "Error: You must be root." 1>&2
    exit 1
fi

for var in EC2_ACCESS_KEY \
    EC2_SECRET_KEY \
    EC2_PRIVATE_KEY \
    EC2_CERT \
    EC2_USER_ID \
    EUCALYPTUS_CERT \
    S3_BUCKET
do
    if [ -z "${!var}" ]
    then
        echo "Error: Environment variable \$${var} not set." 1>&2
        exit 1
    fi
done

apt-get update
apt-get -y install ${build_deps}

for repo in \
    https://github.com/andsens/build-debian-cloud.git \
    https://github.com/sitepoint/build-debian-cloud.git
do
    repo_dirname="$(echo ${repo} | \
        sed -e 's/https\?:\/\/github\.com\/\(.*\)\/\(.*\)\.git$/\1-\2/')"

    # Don't do anything if these cloned repos already exist,
    # in case the user has been hacking away on them.
    if [ ! -d "${repo_dirname}" ]
    then
        if [ "${repo_dirname}" = "sitepoint-build-debian-cloud" ]
        then
            git clone -b instance-store-ami-plugin "${repo}" "${repo_dirname}"
        else 
            git clone "${repo}" "${repo_dirname}"
        fi
    fi
done

cd ./andsens-build-debian-cloud

./build-debian-cloud ec2 \
    --arch "${ami_arch}" \
    --codename "${ami_codename}" \
    --filesystem "${build_filesystem}" \
    --volume-size "${ami_size_in_gb}" \
    --plugin plugins/standard-packages \
    --plugin ../sitepoint-build-debian-cloud/plugins/instance-store-ami \
    --timezone "${build_timezone}" \
    --locale "${build_locale}"\
    --charmap "${build_charmap}" \
    --name "${ami_suffix}" \
    --description "${ami_description}"

Looking at the git history, it seems that I can't decide if euca2ools is a build dependency or not. The answer is that it certainly is a dependency, however I vaguely recall that the version in Squeeze is too old. I'm happy to only support Wheezy now though.