If it's reached the garage roof it must be about 8-10ft high, so what I'd do is get a ladder or steps and start stripping it down from the top ( eye protection is a good tip !) try to work above it so that most of the crud misses your face.
Cut through the stems using a pr of secautres and maybe a hacking kniffe if you have one and pull it away as you work your way down.
Use a weed killer containing 'Glyphosate' which is systemic. It will have little affect by spraying the leaves as the waxy surface will protect it and is easily washed off when the weather does change, instead treat the cut stump and cover it with some polythean to stop it getting washed away, that should take care of it from regrowing.
Good Luck. Tbird+