How many blades do you want to use? You can take a piece of paper and fold it until you have all the divisions or blades you want and then see what size they are. You can make a template from template plastic if you want.
I have also taken a compass and drawn a circle on paper.
Then divide it out til you have all the blades you want. Cut out the blade of paper and add a 1/4" seam allowance to each side and then use that as a pattern to cut out a template on cardboard. Not reall hard. You can use any curved surface like a glass or a DVD to get a curved edge on top or you can make it pointed like a friendship circle.