Your question is very broad, but I will try to give some guidance.
Contact the current ppa owner and coordinate your efforts. You can skin the cat more then one way, probably easiest to make a work group that maintains the ppa. Perhaps the old maintainer can (briefly) mentor you.
If you do not know how to package, I highly suggest you read the packaging guidelines. http://packaging.ubuntu.com/html/
Launchpad / a ppa greatly automates much of the process, but nothing replaces at least a working knowledge of packaging, especially if you hope one day to have your package in the Debian / Ubuntu repositories.
On the flip side, improper packaging often causes problems / compatibility problems.
Next read the ppa tutorial - https://help.launchpad.net/Packaging/PPA