This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
The most relevant parts of the German aviation legislation are paragraph
16 of the 'Luftverkehrsordnung' (LuftVO) (which defines when to ask for a
waiver and what information has to be provided in order to get a waiver) and
Paragraph 37 of the 'Luftverkehrsgesetz' (LuftVG) (which demands that
model aircraft up to 20kg has to have an insurance good for 2.5 mio DM per
accident. If you plan bigger rockets: The next category is aircraft up
to 1200kg and requires a 5 mio DM insurance.)
If you plan to get a distinct area registered as your 'Raketenflugplatz' get
a copy of the 'Richtlinien fuer die Genehmigung von Raketenplaetzen.'
Read it, and decide if you can meet the requirements.