So this is what you are looking for. An empty DVD spool. I buy my DVDs in bulk so I get them cheaper. Ask a stationary shop if you don't have it.

Open it and remove the middle rod from the bottom part. Some rods are screwed and some are fixed on the bottom. If its fixed, cut in circle around the rod with a knife and take it apart. Be careful.

Cut a hole of the size of the rod on the bottom part. Do it right below the big hole from where you cut the rod out. Make a bigger hole above the middle hole. The bottom part should look like this.

Put the rod in the small hole from the opposite side. So when you put the spool back together, the rod sticks out of the container.

The bottom part should look like this from below. The bird is going to perch on this rod.

The bottom part should look like this from above.

Glue the rod like shown in the picture and let it dry. If you don't have glue, you can use small nut bolts too. Check if it's glued properly and can take a little weight of the bird.

Put the spool back together. Cover the spool with newspaper and tape it so that that it becomes dark from the inside and light doesn't get inside from the "walls" (container). Cover the backside also.

I made two! One to gift and one for me! Put a few hole and tie it with wires to high place in the garden. Make sure cats can't reach there. Wait for a few days and keep the camera ready!

And a few days later, my effort was successful as a Brahminy Starling (Sturnia pagodarum) nested in the birdhouse. I covered the container with brown tape so it looks like tree bark.