I loosely followed this tutorial at Splitcoast Stampers. I modified the waterfall strip to 8.5"x 2" which I scored at 2", 2 5/8", 3 1/4" and 3 7/8" to create steps that were 5/8" instead of 3/4" to make better use of letter sized cardstock. I left out the extra layers on the waterfall images as well which gives the card a different look. On the samples here I used stamping and a cut out element on the black and caramel card and a stamped serendipity technique (One Sheet Wonder) on the other. I also created ones with colour printed letters (baby and bday) and stamped images (flower and butterflies). The waterfall images are 1 3/4" square. A stamped greeting can be added to the back portion of the waterfall.
If you have not tried making one of these you should. They are so dimensional when the waterfall is activated!! Check out the video link on this post a few days ago to SEE how cool the waterfall is!!