I have to make a confession. I was fully intent on making this block using the strip piecing method and having it be a miserable failure to prove that foundation piecing would be the preferred method.
While I still think you would probably get a more accurate result by foundation piecing, I was pleasantly surprised by the result I got from strip piecing. With a little more attention to detail it could have been darn near perfect. (And it was nice to take a little break from foundation piecing.)
From your main fabric cut 4 strips 5" x 1 ¼"
From your background fabric cut 3 strips 5" x 3/4"
Attach a background strip to 3 of the main fabric strips along the long edges.
Complete the section by attach all the strips to each other. The resulting section should be 4 1/4" wide. Make sure it is or the "squares" in your final block will not be square.
Cut the resulting block section into four strips 1 1/4" wide as in the photo.
Out of your background fabric, cut 3 strips 3/4" x 4 1/4"
Attach these strips inbetween your "prison bar" strips, resulting in a 4 1/4" x 4 1/4" square section.
(Notice the inaccuracy on the edges because I didn't check the width of my original block section.)
Out of background fabric, cut the following strips:
One 7/8" x 5"
Two 7/8" x 4 5/8"
One 7/8" x 4 1/4"
Attach these around the edges of your square section in a log cabin fashion. (Start with the shortest strip and then attach the others one by one clockwise.)
You'll notice that not all the squares in the "jail" are exactly square. This is 100% due to the fact that I didn't measure the original large section I made (in the 3rd photo from the top).
I'm still quite happy with how this block turned out.