If you want to volunteer and help with developing Log4PHP, you are highly encouraged to read Apache getting involved . If you have questions on that document, we might be able to answer them on the developers mailinglist.
Craig R. McClanahan posted an interesting mail to the Apache Commons mailinglist. I modified the post to fit for Log4PHP:
The best way to contribute is to identify for yourself things that you think are broken, or could be improved, and then propose a patch. A couple of ways to identify possible candidates: