Report generation is done in a separate thread, so there is no event created when the reports finish.
However, what you can do is create a new report
generator. Right now, there are 5 report generators: CheetahGenerator, ImageGenerator, CopyGenerator, FtpGenerator, and RsyncGenerator, generally run in that order.
Create a new generator that does what you want, following the pattern of an existing generator (say, FtpGenerator). Then create a report which runs it. Look at the "FTP" report, which does something similar. Put your "report" at the end of all the other reports, and it will be run last.
That's a brief description. Let me know if you have any questions.