Firstly, you will need to cut the brim of the hat out of cardboard. I recommend a piece that's at least 30cm x 30cm that you can draw a circle on. You may need a compass in order to make a good circle. The circle you draw should be around 24cm in diameter. Cut around this circle using either scissors or a knife. Next, the hole your head will go into. Measure your original circle and draw a dot directly in the middle, this will act as a reference point for the hole. From this reference point, use a compass to make another circle around 18cm in diameter. You may need to adjust the size of your brim to fit your head though. After cutting this circle you should have a ring shape. Keep the disc you cut out for later.
All you need to do for this step is roll a piece of paper into a tube shape. I recommend using sturdier paper than standard. You may also use coloured construction paper to make your hat unique. Any designs you want to put on your hat you must draw before rolling the paper. The diameter of the cylinder should be the same as the diameter of the hole. Cut the cylinder to the right size using scissors and attach the ends using tape or glue. Then, attach the brim to one end of the tube using tape or glue like in the photo.
Use the remaining circle you saved earlier to cap off the open end of the hat. Like the brim you can either use tape or glue to do this.
This is the point where you can add any decorations. You may tie a ribbon around the hat or do what I did and make a chinstrap to prevent the hat from falling off your head. To do this, punch 2 holes on opposite ends of the brim, measure a good amount of string so that it fits firmly on your chin when your'e wearing the hat then tie a knot so that the string doesn't fall through.
You now have your very own paper top hat. Feel free to make any modifications you want. Enjoy!