I am about ready to knit the Ropes and Ladders scarf found here: http://pieknits.com/pattern2.html . I'm using the exact same yarn from the pattern but I would like a wider scarf. Do you think this pattern would look nice and be wider with a size 11 needle instead of a size 10? Will I need more yarn? I am usually a tight knitter, if that helps.
It might not make it much wider, possibly an inch. Try it on the larger needles for a couple inches, see what it measures. You could add more stitches, one on each end (2) for k3 instead of k2, and another 2 on the edges of the cabled panel for a total of 4 more. That and the larger needles might get you a couple inches. Play around with the pattern on scrap yarn, adding the extra stitches so you can take notes of what you should do with those in the cable panel.
I tried using a size 11 needle and added a stitch to both sides of the cable. It's rather curly (needs to be blocked) so I can't tell the exact width but it appears to be a tad over 6 inches wide. Just where I wanted it.
I'd just add five stitches or so on either side of the cable to make it wider. I don't think using a larger needle will do it the way you want to do it, unless you're using a wider yarn, as well. Otherwise, I'd just add the stitches, or another cable repeat or something.