Castle with waste cardboard boxes and cereal boxes.
You need:
Cereal boxes of various sizes, cardboard, newspaper, pencil, scissors, scale, glue. Paint and brush.
Position the cereal boxes on a piece of cardboard and glue them together. cut out cardboard pieces to form the shapes and stick them in place.
Once they are stiff, cover them with newspaper.
You can also give am coat of white paper coat if you wish to get a smooth white base.
Use poster/acrylic colour to give a first coat. Once it's dry, you can give more layers of paint till you get a fine appearance.
Draw/cut windows and doors where ever required and paint them too.