The Ice King costume for sale in Halloween stores is a one size fits all (Impossible!!) and has a full mask but my wearer didnt want to wear a mask, so I made him a costume myself. Here is how I did it.

Materials:
butcher paper or bulletin board paper to draw pattern on
blue fabric
White fur fabric to look like hair
Needle and thread
Cardboard crown from somewhere like Buffalo Wild Wings
Paint and brushes
Hot glue gun and sticks
pencil
scissors
blue and white face paint
spirit gum or fake eyelash glue

Step 1: Ice King's Robe

Ice King's robe was made by following the tailored robe pattern from this site:
http://www.servantsofthelight.org/knowledge/makingrobes.html

Just follow the instructions and take the measurements of your wearer to use when you draw your pattern on the butcher paper.
Cut out the pattern and trace it on your fabric. Cut out all the pieces and follow the instructions to sew the robe.

I left off the hood and didnt put in a zipper

Step 2: Ice King's Crown and Hair

Ice King's crown:
1. get a crown from a resturaunt like Buffalo Wild Wings and reverse it so that the blank side is facing out
2. Cut it into the correct shape (See photo)
3. Paint it yellow
4. Paint the red Jewels

Ice King's beard and hair:
1. Size the crown to fit wearer
2. Get white furry fabric that sorta looks like hair
3. Draw the beard shape in the correct size for the wearer and repeat for the hair. Cut it out
4. Have wearer put on crown and line up hair to center with back of crown. When in correct place, remove from wearer and hot glue hair to inside of crown in back.
5. Test the fit and adjust if needed, then line up beard and mark where the face, mouth, and ear holes should be. Remove from wearer and cut out holes.
6. put on crown and align beard again. When it is right, remove from wearer and hot glue beard to inside of crown in front.
7. Test the fit and mark where to glue the beard to the hair under the ear. Remove and glue.
8. Test fit and correct any issues

Step 3: Ice King Final Touches

Now we need to put it all together.

First mix up some blue and white face paint to get a nice light blue shade to match Ice King's skin tone. Use it to paint your wearer's face and ears. Then have your wearer rub some paint into his/her hands until completely covered. Finally use white face paint to paint on some fluffy eyebrows.

Once your wearer is all painted, it's time to carefully put on the robe. Then very carefully put on the crown and hair combo. When it is in place use a little of the eyelash glue or spirit gum to hold the mustache in place against the face.

And now you have a totally wicked cool Ice King that is much better than the store bought kind :)