Get a hood that you like and trace it on pattern paper. Don't make it too long because there will be a cowl underneath it
Cut it out.

Make a chain just a bit shorten than the pattern.

When you start singlecrocheting the first row you will see it gets a bit longer.

I only crochet in the last loops to give the work a bit texture and make it less heavy

Go on with making rows until your pattern needs to make the round shape. Skip the last crochet in the row every two rows so one side stays straight.
Finish when you find your work matching the pattern. It could happen that you need to do rows over to get the shape you like.
MAKE TWO OF THESE SHAPES

Sew the two pieces together

turn around and you have your hood tadaa

Crochet a scarf. Mine is about 140cm.
Fold it in half and sew the ends together.

When sewn together turn it around
You will get a seam.

Lay the hood (good side on good side) on the cowl
Start sewing them together in the middle so the seam of the cowl and the seam of the hood go over in each other (good English?)

Finish it by cutting of all the unneeded yarn or waving it trough your work.

tadaaaaa

And of course you can wear it down too