This is something a lot of our customers have been doing for years and every year people ask us about doing this. It's very simple really and that what make up the best ideas..
Like most of these projects the toughest part will be getting the wire from place to place. This Project simply involves taking and receptacle box and mounting it up in the eves or some other convenient spot near the roof line. Be sure to use a box suitable for outdoors in surface mounting, or take it a step further and use a recessed bow for a cleaner install. You should also be using an In-Use or Bubble cover like the Carlon or Intermatic ones we have on our site along with a GFCI receptacle unless the circuit is already GFCI protected. Adding an switch indoor is optional but a great way to automate this project. Obviously you could easily use a plug in outdoor rated timer like this intermatic one. As with and electrical installation please abide by NEC regulations and any local codes that may supercede those set by the NEC.