Although I haven't (yet) made an Inverness cape, I too have been researching them, and, from my reading they usually don't have sleeves. The cape should extend the length of your arms AND shoulders, from neckline to wrists. One post I read was using Butterick pattern # 3993 ( though I haven't personally checked it). There was also a former post, here on Xmarks, that was from, I think, something called "The Cutter's guide", which showed how to draw up your own pattern, to fit your measurements & included scanned copy of the draft pattern, to be adjusted to your specific measurements - and then instructions on how to make it.