A costume prop should support the character without making the outfit difficult to wear. Start by checking the event's rules and deciding how the prop will be carried, stored, and used for photos. Choose a lightweight material suited to the shape, such as cardboard, soft foam, or fabric-covered forms. Avoid sharp points, heavy components, and features that could cause harm if the prop is bumped in a crowd.
Sketch the prop at the intended scale and test the grip or strap with a rough mock-up. Consider whether you can hold it for several minutes, put it down easily, and keep your other hand free. Smooth or cover rough edges, and use color and surface details to suggest depth without adding unnecessary weight. If assembling with adhesives or tools, follow their instructions and work in a suitable, well-ventilated space.
Before the event, practice walking with the prop and moving through doorways. Make sure it does not block your view, catch on clothing, or interfere with other people. A simple carry loop or secure sheath can help when the prop is not in use, provided it does not create a snagging hazard. Clean and inspect the piece afterward, then store it so it will not bend or crush. Clear rules and comfortable handling matter more than exact realism.