You can use this method for making a hooded shirt from scratch or for reconstructing an existing shirt.
If you are making your own pattern on the fly, I’d suggest finding a hoodie and tracing the hood, making sure to add a seam allowance. You may need to alter the hood to fit the top you want to sew it to- just remember that the bottom edge of the hood should be the same length as the measurement around the neck hole.
Your hood pieces should be sewn together before you start, and the edges finished. You can hem the edge or trim it with contrasting fabric or lace.
You can also line your hood. Cut two pieces of lining fabric the same shape as your hood. Sew the lining together. Then sew the lining to the hood, right sides together. Don’t sew the “neckline” edge of the hood and lining together. Leave that edge open so you can turn the pieces right side out, and then baste along the neckline before sewing the hood to your shirt.
Your two pieces here are 1. the hood and 2. the nearly finished top. mark the center of the bottom of the hood (green dot). Mark the back center of the neckhole of the top (green dot).
The front edges of the neckhole of the top have been marked with yellow and pink dots and the corresponding spots on the hood are marked as well.
Match these points up. The hood should be folded around the shirt, with the outside of the hood facing the outside of the shirt.
Start sewing at one end of the neckhole, and sew until you’ve reached the other side.
You’re done! This is what it looks like with the top opened up.
This tutorial was for a hoodie with a zip front, but the process of attaching a hood to a top without a zip is pretty much the same. Just overlap the two edges of the hood a little to get continous coverage all the way around the neck.