As robots' capability and autonomy improve, they are expected to increasingly operate in human environments, and interact with novice, untrained users. When robots operate in human or shared environments, their tasks and behaviours need to be specified; this task is typically performed by a human operator or supervisor. The human operator may specify constraints on robot behaviour to make the robot more predictable or align its behaviour with user expectations. However, these constraints may impact robot task performance. This paper investigates how novice users generate robot specifications and proposes metrics for quantifying specification quality. The proposed approach is evaluated with a user study, where novice users provide specifications for an autonomous robot operating in a shared warehouse environment. We find that untrained users create a wide variety of behaviour-limiting specifications, that users generally have difficulty creating efficient specifications, and that they were not able to correctly assess their own performance.