Make a CoreOS Image following the guide here
Tell it where to get it's cloud-config file (should be an URL), or use the example:
make example
Which does this, which you can do manually:
cp USER_DATA_URL.example USER_DATA_URL
then set up the network, or use the example
cp NETWORK.example NETWORK
then set the mac address, or use the example
cp MAC.example MAC
If you like you can have it pull user_data so you can edit it
make coreos1
edit the user_data now
vim coreos1/openstack/latest/user_data
now finally run it
make run