You can for example use https://www.ebay-kleinanzeigen.de/,  https://jasprtrades.com/, the local recycling company, https://www.freecycle.org/, the projekteverteiler Leipzig and other sharing websites

good luck!

Things that are needed:

• building material:
• plastering, Putz
• electrical cables, Stromkabel
• waterpipes (steel, 1/2 and 3/4 inch), Wasserleitungen (Stahl, 1/2 und 3/4 Zoll)
• ladders
  
  
• living/office material: 
• matresses,
• bedding plus sheets and cushions,
• kitchen (probably two) plus everything needed for it like pots, pans, cutlery, herbs and spices,
• wardrobes, shelves
• tables, chairs
• lamps and bulbs