Cover a table or work surface with newspaper. This will protect the surface throughout the process.
Blow up a balloon, and tie the end into a knot. Make the balloon as large as you would like the nest to be.
Place the balloon, with the knot facing down, into a bowl.
Cut pieces of old fabric into strips of varying sizes. You can use old T-shirts, ribbons or other fabrics.
Pour some craft glue into a bowl.
Apply a coat of glue to the back of each fabric strip, using a paintbrush.
Drape the fabric strips over top of the balloon, forming the shape of a nest.
Allow this layer to dry for 30 minutes.
Cut up pieces of string, of varying colors and lengths.
Dip the string into the craft glue. Wear rubber gloves while doing this to avoid getting glue on your hands.
Place pieces of string over the top of the fabric layer. You may choose to cover the entire fabric surface, or to drape only a few pieces of string over top. It does not have to look neat, as robin's nests typically have a very natural and unpredictable design.
Allow the nest to dry and completely set. Let it sit between five and eight hours for the best results.
Flip the balloon right-side up, and pop it with a pin. You will be left with the robin's nest. The nest can be filled with some rose petals or artificial robin's eggs and put on display.