Polycarbonate rafter support bars are made for 10, 16 and 25mm polycarbonate. They feature an aluminium base and a plastic cap which locks in with teeth to easily join your sheets together. The widest sheet of polycarbonate is 2100mm wide but bear in mind that this would need to be supported approximately every 700mm for snow load.
Rafter support is the more economical system to use so that you can use wider sheets and less bars on your project. With self support bars the longer the length the narrower the sheets will need to be take the overall load.