for long lasting assembly, use both screws and nails and use wood glue.
when attaching the angle iron, use some kind of adhesive(glue, silicone, chalk) in addition to screws this way it will never fall off.
also, weather proofing it(i.e. thompsons water seal) will help it endure rain/sleet/snow and also helps it make the surface a bit slicker.
*warning, do not skate weather proofed wood with even the slightest bit of water on it, you'll die!*