Like Jeremy, I havn't been able to get the free version to even download at all.
Try again just draw a simple rectangle then select the top face, go to plugins menu click instant roof, pick a style, and OK the default settings work fine for now. Jeremy, not sure what happened to your download, I just downloaded the script, installed it and in less than 5 minutes, I had a roof.
Maybe its because I don't use Google SketchUp Pro. I'm trying to download the free version, but its not working. Very cool plugin, however I found the Instant road plugin even more fun.
