Make a list of the props you will need for the play. The easiest way to do this is to simply go through each page of the script and note what items appear in each scene.
Determine what materials are available to you. You may have access to school materials such as paint. You may need to buy some of the materials to build your props and should factor that amount into your budget.
Enlist students to help build props. You can recruit actors, as well as members of the stage crew. Depending on the age of the students involved, you may need to ask parents or teachers to oversee the project. An older student or an adult should do any building requiring tools.
Check how your props look from out in the audience. While your props may look great up close, you may need to make them larger or give them exaggerated characteristics for audience member to see them from a distance.
Appoint a member of the stage crew to be responsible for the props. This person will keep track of props in between rehearsals and performances. He also makes sure that they are available for the appropriate scenes.