For the box itself, you really can't beat the old reliable military ammo can. These boxes are cheap, sturdy, and waterproof. I've got a couple of them I picked up at a surplus store who-knows-how ...

Make sure you understand how light switch wiring works, what color wires do what, and how to switch the mains power on and off at the fuse box. Turn the mains power off at the fuse box.