The following steps apply whether you are making a hat from paper or fabric. For your first attempts, use paper and experiment with adjusting the hat pieces to make different styled hats. When you have a hat style you like, you can make it out of fabric by printing the pieces with your computer printer, or by using the pieces as patterns for a fabric of your choice. For lightweight fabrics you can use fabric sizing or starch to give the fabric body to hold it's shape, or you can iron your chosen fabric to a lightweight iron on interfacing to give it more body.
Start Making The Hat by Shaping the Top Brim.
The hat brim needs to be adjusted to give it some shape rather than leaving it completely flat. Adjust the shape of the brim by creating a narrow or wide overlay at the back seam where the line was cut through to the brim center.
To Adjust the Fit to a Doll's HeadIf the hat will be worn by a particular doll, or over a particular hair style, fit the hat brim slightly loosely to the doll's head before proceeding with any further steps. The fit will become tighter as you add a second layer of paper for the lining, so the first fit should be slightly loose. Before you glue the hat brim, check that your circular crown piece is large enough to cover the opening for the head in the brim. If it is not, you will either have to adjust the size of your brim and make the opening smaller, or cut a larger crown piece from a different scale of printables.
When your brim is the correct shape and size, glue the overlapping areas of the brim together and set aside to dry.