LeviProps are tangible structures used to create interactive mid-air experiences. They are composed of an acoustically- transparent lightweight piece of fabric and attached beads that act as levitated anchors. This combination enables real- time 6 Degrees-of-Freedom control of levitated structures which are larger and more diverse than those possible with previous acoustic manipulation techniques. LeviProps can be used as free-form interactive elements and as projection surfaces. We developed an authoring tool to support the creation of LeviProps. Our tool considers the outline of the prop and the user constraints to compute the optimum locations for the anchors (i.e. maximizing trapping forces), increasing prop stability and maximum size. The tool produces a final LeviProp design which can be fabricated following a simple procedure. This paper explains and evaluates our approach and showcases example applications, such as interactive storytelling, games and mid-air displays.