There are many free patterns for Do it Yourself felted hats on the web. Many start at the crown and increase for the shape, others start at the brim. Most are knit circular, but can be knit flat and seamed. I think it is a matter of choice as to how you like to knit.
I’ve chosen to use Istex Lette Lopi, an aran weight yarn which blooms so beautifully. 100 gm per hat. I work from the brim to the crown. They are handknit.
The felting process was in a domestic top loading washing machine, using detergent. 3 cycles were needed to achieve the sizing.
It is a bit of trial and error to achieve the desired shapes and brim depths.
My hats are available for purchase. Contact me if of interest.