I made a lap quilt with this pattern using a jelly roll. Loved it, and so did everyone who saw it. But, a couple of tips I learned on making it.
First: Like MTS said, not all strips are the same. I had a jelly roll, but found that the middle was larger then the ends. Yes the ends were the right size, but I had to cut the middle down some.
Second: If you watch the Missouri Quilt Co video, they first make it by sewing strips together, then cut the triangles. I didn't have the triangle ruler they showed, but I found that I could use the corners on a square (I had a 12 in x 12 in ruler and used painters tape to help keep the same size for each triangle). This makes quick work!
Last: The squares were bigger than I expected!! When my finished 4 squares were sewn together, the block was about 16 1/2 inches or so. I could cut them down and still had a great looking square!
Good luck and enjoy!