You don't even have to build the package. You just create a source package and upload it with "dput" or similar. Then the PPA servers will build your package fo

You don't even have to build the package. You just create a source package and upload it with "dput" or similar. Then the PPA servers will build your package for multiple architectures (usually x86 and x86_64, but a Debian PPA might build for all Debian architectures, which are many more). It is also possible to build for multiple versions easily by changing the target distribution in the changelog file. I've done the above both with and without a PPA for Ubuntu. Without a PPA you need to have separate virtual machines for each architecture (and if you don't have physical machines and/or hardware virtualization, this will be really really slow). And you also need a VM (or perhaps a chroot/pbuilder environment) for each distribution version, if you target more than one version.