A good way to start your KDevPlatform plugin development is to use our plugin example. This can be found in the KDE's kdeexamples repository, you can get it here:
$ git clone git://anongit.kde.org/kdeexamples
In the KDevPlatform directory you will find the example that we have available right now. ProjectView is a good way to start because it displays how to add some UI and interact with the shell to get some of the available information.
You can just import it with KDevelop and start playing with it :).