I was going to suggest a Yellow Brick Road pattern. It uses three blocks: one with three pieces, one with four pieces, and one with five pieces. You can make it as long as you like by making more blocks. Because it's made with non-identical blocks, and because you turn them different ways, the resulting easy quilt looks difficult to make, and it's a very interesting pattern.
KwiltyKathy-- thanks for the link to the QR code maker. That's awesome for a teen!
Prism--I love the quilt you linked us to on Craftsy! Thanks!