Draw an isoceles triangle on a sheet of newspaper with the base of the triangle 11" (head measurement/2). Make the height of the triangle something that pleases you.

Add seam allowance to the sides of the triangle… 3/8" to 5/8" would be conventional. Draw straight lines 1.5" and 2" below the base of the triangle. Those will be the hem of the cap.

Cut out your newspaper pattern. Fold the hem portion of the pattern up, folding 1/2" under. Take your scissors and cut the folded hem along the lines for the sides of the triangle. Unfold. You’ve got your
pattern.

Cut 2 pieces, with the base of the isoceles triangle along the crossgrain of the fabric (very important… wovens stretch more on the crossgrain than the lengthwise grain). Sew the side seams; press. Turn up the hem, press. Wear.

The reason you’re not finding much in the way of patterns for wovens is that they tend to slip off at night. Some old timers had earflaps and strings to tie under the chin of their flannel nightcaps.

References :
50 years of sewing; amateur patternmaker and draper.

http://www.ehow.com/how_2181846_nightcap-sleeping.html

If I find another I will come back and edit.
here is one for fleece
http://extension.usu.edu/files/publications/publication/FL_ST_Construction_2006-301pr.pdf
References :

I found one for a goose. You may be able to enlarge it on a copier to the size you need.

PJ
References :
http://www.webstitch.co.nz/freehat.html