I tried so hard to find good pattern for my granny square pillow. Finally, I found granny square with circle center by Blair Stocker.
This pattern is written well and very easy to follow. For each side of my pillow, I made 25 grannies(5x5). Front side I used green and blue tone combination and colorful color for another side (I wanted to clear my yarns stock)
However after you finished your grannies,you need to join each square with good method.I recommend this Youtube VDO to join them with single crochet.
Someone prefer to shows the Sc stitches outside but I want to have the plain one so I joined them from the wrong side.
P.S. when I joined 2 pieces of pillow together, I made single crochet only 3 side, put pillow inside and close the pillow from right side.