All it takes is about a yard of fabric to make a cute, custom pillow case. My sewing skills are very lacking, but this is all straight lines, so it is super easy. All you need is:
Scissors
Ruler
Thread
Fabric (I used about a yard of one, and about a quarter yard of another.

Step 1: Make a "Pattern"

Using a pillowcase you already have, measure the rectangle to find how big you need to make yours. Mine was about 20 inches wide and 30 inches long. Afterwards I googled the "standard pillowcase size" and found that most are about 22 inches by 32 inches.
I decided I wanted a little bit of contrasting fabri on the edge of mine, so I decided 5 inches of the 30 were enough. I added 1 inch seem alowance on all seems, and an extra 3 inches to fold over on the open edges, since that seems to be standard for all pillowcases. So, I came to decide, I need 2 pieces of the "main" fabric, 22 inches by 27", and 2 pieces of the "accent" fabric that were 22 inches by 9 inches.

Step 2: Cut Fabric

I cut the fabric, 2 pieces from each. The Bill and Ted fabric is my "main" design, and the green is the "accent." Because the flash went off in some pictures, and not in others, the color seems to differ from blue to green, but the solid fabric is all the same.

Step 3: Pin the Fabric

Right sides together, pin one of the "main" fabrics" to one of the "accent" fabrics along the side that is 22 inches.

Repeat with the other two pieces of fabric

Step 4: Sew

Sew along the pinned line on each pair of fabric.

Step 5: Make the Opening Hem

Fold the "accent" fabric down 3 inches and pin along the line. Repeat for the other panel. Sew along the pinned line on both panels.

Step 6: Pin the Panels Together

Put the panels right sides together with the blocks of fabric matching. Starting at one corner, pin around the edges, leaving the top part (the part with the 3 inch hem) open.

Step 7: Sew Around the Panels

Starting at one corner, sew along the edges, making sure to back stitch at the begining and the end. Clip the ends of thread.

Step 8: Done

Turn the pillowcase right side out. Put the pillow in, and you are done.

I made a UNC pillowcase for my husband for Valentines day, and a Spongebob one for my son's birthday. They are quick and make good gifts.