Prepare a large sheet of construction paper (e.g. 24" x 36") to make into the sombrero's wide brim. Red, yellow or any festive color works best.
Place the plant pot upside down at the center of your construction paper. Use a pencil to trace the outline of the pot's mouth on the paper.
Draw a pair of perpendicular lines, intersecting at the center of the circles. These perpendicular lines are just guides to help you draw an oval brim.
On each of the four lines, mark the point where you plan to draw your oval, thus defining the size of your hat's brim. Opposite points must be roughly the same distance from the center.
Check on your plant pot. Once the white paint is completely dry, use poster paint or acrylic paint to paint the pot with your intended color or colors for your sombrero's top.
You can make the top and brim the same color or use contrasting colors. Bright red, yellow, orange and green are popular colors in Mexican art and culture—I used this color palette to paint stripes on my sombrero top.
Cut a length of elastic string to make a chin strap for your hat. Use transparent tape to attach the ends of the string on the inside of the pot. Adjust the length of the string for a comfortable fit. To make sure the string stays in place, you can secure the ends with a glue gun instead of tape.