Yes the pattern for ATOC will work well for the shadowguard or the TFU royal though and since the reference material even states that the outer is based on the ATOC robes then it is fine.  
Even so I believe that the Rogue one pattern will work better.  
 
Look at the image below then compare the two outer robes.
https://68.media.tumblr.com/7588c7b160a ... 3_1280.png
Let me explain.  The two arm slits wrap around more towards the back with the ATOC pattern but when you look at the official renders of the character you'll notice that the two arm slits end just under the helmet.  When you look at the official reference materials you'll notice that the front arm slits do not match up with the ATOC pattern and that is most likely why the official material says that the design was "Based" on that style.  Rogue one came out afterwards and when you compare it to the official reference images you can see it appears to line up much more closely than the ATOC pattern would.  
Take a look (click on the image to see the larger version):
 
The one suggestion I would like to make is that once the slit is made in the back that the top 3 to 5" be left and the place where the split ends be reinforced.  3" should be plenty to allow the outer to be hidden underneath the back of the helmet and the reinforcement will hold it together when you go into "combat ready stance."
You have 2 options when it comes to your outer robes and sewing the lining into it.  Either method works.  The liner can be sewn closed on all sides or left open along the bottom.  If the liner is sewn closed then you will need a handler to help get some of the odd folds which happen because the liner creeps/moves and tends to hold the folds from when you move.  If you leave the bottom of the liner open and properly trimmed then the outer will have a more natural "flow." and won't require as much handling to keep you looking good.  The only real issue is that when you're in combat ready stance the liner may hang just a little bit too long in a couple places. (Not an issue when the robes are worn as a standard guard/draped)  So each method will work and it is personal preference as to which method you choose to follow.
The reason for this is because the TFU guards are part of a digital medium and the material behaves differently there than it does in the real world.  What we have to do is make the decision as to how to portray the character.  You can also sew some weights into the bottom of the outer robes to help with the flow and overall appearance; however, my outer is already 35Lbs without adding those fabric weights.  Regardless of the method you decide on you will need help with the front panel and getting it to sit correctly across your shoulder.  What I have been doing is lifting up my helmet and then having my handler arrange the front panel over my shoulder and then we sit/clamp/push the helmet down over my head.  Be aware that you will get INSANELY hot with that panel held in place that way.  Then again you could sew a couple small pockets into the outer (Must be 100% hidden no stitches showing etc.) and hide some of those super strong magnets in the robe and have a couple really strong magnets hidden underneath your backplate as well.  I've been thinking of doing that with mine but don't want to dig out the seam ripper.
So with all of that said I wish you the very best with your shadowguard outer robes.
 
