Step 2: Create Template
Draw a Butterfly the size and shape you want to make on a piece of paper ( any type of paper will do). Add lines to define the patterns on the wings - this will be used in the next step.
If you can't draw a butterfly i am sure you could find lots of pictures online.
Cut out your paper butterfly. This will be your template
Cut the plastic bottle into squares roughly the size of your template
Place the paper butterfly template on the plastic square and cut the plastic to match the template
Repeat as many times as you want
now you have a bunch of plastic butterfly shapes