I would knit up a swatch in whatever you’re using with the cables. Figure out how many stitches per inch you are getting, measure how big you want it to be and cast on # of stiches = stiches per inch x measuremnet of how big you want it. Voila. I would use the pattern that you ahve as a guide. You can do it
Here’s a pattern for a hooded scarf (it’s a webpage with a bunch of patterns on it. I think they’re all PDF files but they’re free) you can just add cables to it.
There is a pattern for a hooded scarf in the baby knits for beginners by Debbie Bliss. It is just a plain scarf, but you could change up the pattern like feministmama suggested by adding a cable.