Fold paper down middle hot dog.
Fold the paper a bit from bottom horizontally.
Fold it again horizontally about 5 inches from the top.
Measure a ten each line on each horizontal fold,
making sure the center (5 inches) is on the vertical center fold.
Mark every 1/2 inch on each line.
Draw a curved line from the top left line to the center line.
Make curves that go from the top center line to each 1/2 inch mark on the top line.
Do the same on both sides.
Add a door in the middle and details to make the cage fancy.
Look on Google Images for "Birdcage Clipart" for ideas.
Outline all lines with a black marker when done.
Lightly draw a bird in pencil in the cage behind the bars.
Draw another bird doing what you want in or out of the cage.