I have to admit, I had to look up what a ruana is; it is a poncho-style garment. It looks both elegant and comfy. The poncho consists of two identical panels, which are partially attached to each other. The pattern is very easy, with 2 alternating stitches (and a one row repeat).
You can find the free crochet pattern of the Rochefort Ruana on the website of Lulo Stitch Co.