Hi,
Aircraft must be below 5KG, around Airports & Helipads you have a 1.5KM NFZ, outside of the 1.5KM radius around an Airport BUT within a control zone you have a max altitude of 30 meters.
Powerplants, Hospitals, Military sites or areas & Prisons must be avoided, also disaster zones (we have a few in south germany at the moment due to thunder storms) and of course crowded places.
For private pilots, the maximum altitude is 762 meters (here ends the non-controlled airspace) BUT practically the maximum altitude is limited by the viewing distance (LOS).
Chris