How can I build a package for multiple distro series in a PPA?

If you try to upload a package that already exists in a different series in your PPA, it will be rejected. Similarly, using the "copy packages" page and selecting "rebuild" will result in an error.

The problem you're experiencing is because of the pool-based repository format of Debian archives. That is, you cannot have the same version of files published more than once with different contents.

You have two ways around this:

1. Use the "copy packages" feature but do not select "rebuild" - use this if you don't need to rebuild against newer dependencies in the other distro series.
2. Upload a newer version of the file for the other series - use this if you want to recompile the same source against the newer dependencies in the other distro series.

These are essentially the same actions that Ubuntu itself uses.