The revisions that would make the diagram of the fire pit more effective are:
1. Including images for each step of the process;
2. Adding a label to indicate the depth of the fire pit;
3. Including labels for all materials mentioned.
Those revisions would make it easier for the person building the fire pit to visualize the work that has to be done and the way it is supposed to be done. Understanding the materials, their appearance and use is an important step to ensure the success of the project. Since the depth is crucial for the fire pit to function properly, being able to visualize the correct depth is also essential for the building. The pictures of each step would help eliminate possible doubts, especially if the images are well depicted and numbered.