When you upload your source code to Launchpad, it is being placed into the queue, depending on a point system (usually the more important the package the more points it has). As it is mentioned here: https://help.launchpad.net/Packaging/PPA/BuildingASourcePackage you have to use
debuild -S and then upload your source via the
.changes file that is being created.
So, what you have to understand is that a package isn't being built by launchpad exactly when you upload your source code for building. So you have to wait some time (usually 10 mins to 1 hour). Then Launchpad starts building your source code into a DEB, depending on what you have specified in your
debian/control file. For example, if you have specified that your package is only for the i386 architecture, then it will build a package only for it, but if you have specified
Any architecture, then it will build for both i386 and amd64 architectures. The supported architectures are listed here: https://help.launchpad.net/Packaging/PPA#Supported_architectures
Till the package is waiting at the queue, it will be at the "Needs building" state, and, as you can understand, the DEB packages haven't been created yet. If the building process is finished, then launchpad provides you with the DEB packages that it produced. You can see the DEB packages on the 'View Package Details':
and then you click at the arrow on the left of the package:
Basically, you can use this so as to build your packages to all the available architectures if you have an i386 machine or so as to distribute your software to more people using the
add-apt-repository method. With this method everyone will be able to receive updates from the specific PPA.