Send digital pictures of it to robertwhiting76@hotmail.com and I might be able to see what you can do as a temporary job without it I could only guess a repair. Think of house insurance it may cover the garage roof being attached.
Effecting electrics: Find source cable disconnect if you feel confident enough to do so if not call electrician.
On a dry day ONLY.
Turn on the garage lights then turn off the house FUSE feeding downstairs lights only NOT the master switch on the fuse box. If garage lights are also off then that's proved the garage light/s are on that fuse.
You now have the job of finding the feed cable from the house to the lights or to a junction box then lights. That feed cable should then be disconnected and he wire put in to 3 segment electrical strip and well wrapped to keep out water and tack up away from the leak and possible prying hands.
If you still get the lights problem in hous then it's serious requiring electrician.
Bob
January 2009