If Europe decides to draft a federal European constitution, I highly recommend that you study features within the Earth Constitution, what I consider to be the "gold standard" for a federal democratic world constitution. Drafted by the World Constitution & Parliament Association, the Earth Constitution is superior to the US Constitution. Democratic World Federalists (dwfed.org) and the Earth Federation Movement (earthfederation.info) share a belief in federalism.
Jakub's Universal Blog Hitting the European nail on its head
Blog by Ralf GrahnSeveral articles about the European Federalist Paper by Ralf Grahn
Leo Klinkers interviewed by Salvador Llaudes