well i got lazy with taking pics but i think it's pretty straightforward.

basically i had bed pillows taht i was using for our couch so for the case i wanted it to have an envelope back instead of an open side

Step 1: Basic Patterning

i traced a pillow case onto the wrong side (ie the side that will be on the INSIDE of the completed case) of the fabric

i just made a marking on the corners.
now remember to leave about 5/8 of an inch for seam allowance (this means that you leave a little space between the tracing of the case and where you actually sew it otehrwise it'll be too small when you turn it inside out)

now for my next cases i got smarter and realizing that the case i traced was much larger than my actual pillows i made it a bit smaller

Step 2: Making the Envelope

k with the piece of fabric that is the back of the pillow case, have the wrong side facing you

then you cut it vertically
(i cut it so that it was 1/3:2/3 for the envelope, but if you want envelope in middle, cut down centre)

then on each side that will be teh envelope. fold in material 1/2" and pin or baste (ie sew loosly like the pic) in place. if it's a material that will fray easily, i recommend folding it then folding it again

sew with machine (if you pinned it, make sure to take out pin before going over area with machine or else needle will break)

Step 3: Putting It All Together

now you put the fabric pieces all together, with right sides facing each other
overlay teh back pieces so that where the opening will be, the pieces are overlayed by like 1.5"
then pin and baste along all the perimetre of your case

sew in machine and you're done!!!

sorry if this isn't that clear, it's my first instructable

try messing around with different materials and textures
and i recommend not having cats around while making it because they will continually chew your thread or lie down on the material