normally i won't post my patterns unless requestedjust because they're pretty useless and complicated to anyone but me, but asked for this one that i used on my sherlock plush ([link]), and it's pretty simple so i thought i could maybe explain it. i'm pretty rubbish at that, as you can see from the instructions above!
this isn't really for a proper deerstalker, just a felt one. if you want a fleece one or something just add extra seams along the bottom and outside the brims/flaps for hemming. i don't know how to make a true-blue hardish thickish hat, but there's gotta be a tutorial for that somewhere. i figured out the pattern mostly by eyeballing and measuring pictures of deerstalkers as i've never actually seen one, but i think it turned out decently. alter as you wish. also, when you sew on the brims and earflaps, make sure you're stitching on the side that won't be seen. for example, since my flaps went up i stitched them on the inside, and since the brims go down i stitched them upside down on the outside.
again, i tried to put some instructions down, but this is pretty basic stuff sorry for the non-digitalness as i am still tablet-less for now, but i tried to be neat traditionally. enjoy!