This was a more structured layout of the pillow... I used 2" strips to give it a uniform look. It really does not matter what size the center starting square is, or even if it is square... but on this pillow I started with a 2 1/2" square.
The back is mainly two pieces that are approximately 10 x 16. I used a contrasting strip to face the edge of the opening, but if you have enough fabric and don't want a contrast you could make those two pieces 13 x 16 and fold over 3" to form the facing. On this particular pillow, I used fabric from another project that had two finished edges, so it was not as wide as I needed it to be, but wide enough that if I offset the overlap, it worked just fine. So the overlap can be whatever you choose. The facing strips are top-stitched on both the opening edge and the edge of the facing that has been pressed under about 1/4".
I pinned the back two panels in place, then I put the pillow front on top and cut the back to the same size as the front. I did not want my corners pointed, so I cut them rounded, which makes turning easier. You can draw a line using something circular (thread spool) that gives you the curve you want... I just eyed it as I was cutting. Pin as you feel comfortable, then start stitching in the middle of one edge that does not have the facing. This is so that your ending stitches are not where they will be pulled apart when you are putting your pillow form inside. The outside seam is continuous. I did not backstitch because I over-stitched about 1" when I came back to the start.
The first pillow I did using a 14" pillow form, I trimmed the top to 14 1/2". I thought it was a little snug. This pillow I trimmed the top to 15" which was a better fit. You could also choose to add a Velcro closure, but I did not use one here.
I don't have pictures of other pillows, and the one issue I saw more than once, was when the strips are being added around the center, even though it appears that they are squarely around that center... as you get close to the edge several ladies found that their square was twisted a bit and they were running out of backing/batting on one or two sides. If this should happen... not to fear, fold your batting out of the way and add a strip to the backing. It does not matter if it matches as it is inside the pillow. It is also not necessary to press that seam open. Next, fold the backing out of the way and butt up a piece of batting to the batting... you do not want to overlap here. With the butt edges as your center line, zig-zag the two together. You can now go back to adding strips on the front. At the start of your project, because this is easy to happen, it is a good idea to make your backing and batting a good 3 or 4" wider than your finished size. Lots of reasons why it appears your batting suddenly has a mind of its own and runs out on you.
Maybe I can get a group picture of all of the pillows when everyone has their pillow completed .