The first thing you need is a good sensitive circuit breaker, an essential for any gear being used out side, as to the actual lights and fittings any decent DIY shop or Electrical Factors should carry a selection of outside equipment,cables etc and most will be happy to explain the correct usage. If you live near a Wickes pop in and have a look thro the pamphlets they usually have about various projects they are normally pretty good, but what ever you decide remember electricity and water can be fatal
so if in doubt double check