When building an image with lorax, it makes a temporary directory in /tmp to do work. With the new tmpfs feature in Fedora 18, the available disk space in /tmp is limited and not enough for image creation. According to the tmp-on-tmpfs feature, anything needing large amounts of disk space in /tmp should use /var/tmp instead of /tmp This issue exists in lorax-18.14-1.fc18 which is current at this time.
Are you using pungi to do the composes?
This package has changed ownership in the Fedora Package Database. Reassigning to the new owner of this component.