The Matrix pattern is a decent place to start for those with little patterning experience, especially in regard to Organization coats. The seams will require a bit of editing, which I'll discuss below, but in addition one will have to construct a hood, which I can only give suggestions towards.
This tutorial assumes the following:
-All seam allowances are 5/8."
-You're using a #30 zipper.
So lets begin!
Initial Pattern Editing
The Matrix Pattern
This is the pattern as it comes from Simplicity. I edited out the pieces that are pretty much useless, so that which remains is what you should mark for cutting on the actual pattern sheets.
This is where those pieces would go should one be making the actual coat as per view 'A.'
Edited Matrix Schematic
And this is what we're aiming to end up with, below.
Piece 1 edit
Piece one requires a fair amount of editing to start with, since the matrix pattern does two things that organization coats do not: It has an overlapping front closure, and it has a collar. On the front of piece one there should be a line indicating where the center of the front is supposed to be(the dashed line in the above picture). Cut along this line on the pattern. This is to get rid of the extra fabric that won't be needed to make the Velcro attachments.
Also, the neckline must be edited to accommodate the scooping slope where the hood attaches, so widen it by cutting along the topmost dotted line in the above picture.
Piece 3+4 edit
Add 5/8ths of an inch to Piece three on the fold edge, and tape it onto Piece 4, overlapping 1 1/4ths inch where its being joined at. This will give one solid back piece to use.
At this point, I would suggest taking the three edited pieces and cutting them out of some cheap fabric to make a mock-up of your coat, that way you can get it to fit properly, and for the next edits that I'm about to suggest. This isn't necessary, as you could theoretically 'wing it,' but its generally a good idea just in case.
Sewing the Mock-up
Sew the edge of A to A, then B to B, C to the other back-pieces C, and finally D to D. At this point, you'll have the basic idea of the coat, but there is still a lot to do to get it right. Take this time to check the fit of the coat...these mock-up pieces are going to become your actual pattern pieces, so if the coat is too loose, sew in more along the sides(D) and back(C) to get it nicely fitted, and then cut the edges to 5/8" from the new seam. Also check to make certain that the scoop of your neck seems about correct. If not, cut it to where you want it to be.
This is about what the coat should look like on you, at this point(minus the sleeves, as you wouldn't need to sew those on your mock-up if you didn't want to). Here is where even more editing fun begins. ^.^
Take a marker and draw in where the red lines are on your own mock-up. The front line should follow the top of your 'pectorals.' The pocket should be aligned with where your wrist lies when resting at your side. The back seam should have a slight curve to it. Other than that, its up to what looks right to you. ^.^
Taking apart the Mock-up
Take a look at the marks that you made, and chose which side of your mock-up looks the best to you.
Take whichever side you chose, and, following the above picture, cut along the red dashed lines and seam-rip through the blue slitted ones.
The New Pattern
This is about what the pieces of your mock-up should look like once it is taken apart. On this piece, go ahead and cut out the 'pocket,' along the red line.
Pocket Pattern Edit
Taking this pocket piece, add 5/8" to the top, bottom, and right(the side towards the zipper), and then cut out two mirrored pieces of these from your actual fabric(or cut it out once with the fabric folded together, to get two mirrored pieces).
Actual pocket edit
Along the top and right, fold the edge under 5/8" and sew to get a nice hemmed edge. Leave the bottom edge alone for now.
Finally, take the pocket pattern piece and tape it back to the bottom of new pattern piece 2, so that everything looks like it does in "The New Pattern" up above.
Before you proceed, you'll have to make a decision on which type of 'piping' you will want to use. Piping is necessary because Organization coats have many 'double seams,' such as those that are shown here:
This picture seems to have an excess of them, however, if we're going by the typical render, so we'll ignore the one on the sleeves and the one on the side-seam.
There are three ways to add these double seams that I can think of.
The first way is to use piping. Piping will give an end result similar to this:
There is a very good page on how to make piping(and also binding) here:
Piping and Binding tutorial
Making piping may be necessary if you chose this route, because it is important that your piping match the material of your coat. Piping is available pre-made at most fabric stores, but generally only comes in a cotton blend that would be unsuitable for pleather coats.
The second way is to actually cut a strip to sew in between your panels, in this manner:
Sewing an ACTUAL Double seam
Which would give the appearance of this:
Or the third manner is to top-stitch a line next to the seam, to give the appearance of a second seam.
The choice is yours. ^.^
Putting it all together...
So now its finally time to cut out everything else!
Final Cutout Pattern
Go ahead and lay out all the other pieces on your actual material to cut. You'll need two mirrored pieces of each, again, which is usually just easiest to obtain by cutting one piece on folded fabric. Pay attention to which way your fabric stretches, if it does, and make sure you lay the pattern so the coat will stretch around you(so the stretch goes perpendicular to the zipper or your center back seam).
When you're cutting out, add an additional 5/8" anywhere that there is the extra blue on the pieces above.
For the sleeve, if you are making the sleeve of anyone but Axel, Xigbar, or Demyx, you'll probably want to make it wider, so follow the blue marks on the sleeve pattern. For Axel, Xigbar, and Demyx, the sleeves are relatively tight, so adding extra would be a waste.
Sew piece 1 to piece 2 along the green line. Don't forget to add in whatever sort of piping you're using!
Sew Back Flap and Pocket
Sew the pocket onto piece 1 as follows(its a funny color because its upside down) along the green dotted line, and also sew piece 3 to piece 4. Again, when sewing piece 3 to piece 4, don't forget your piping!
Flip the pocket upright after its sewn until its top rests along the red line(or where the red line was on your mockup pieces) and either topstitch the pocket down or glue it on along both of its edges.
Nicely enough, if you leave the top edge of the pocket unstitched, you can reach your hand into it. ^.^
Sewing the Rest
Once you have two single front and back pieces and a sleeve piece, you can pretty much finish the rest of your sewing in one shot. A to A(front shoulder to back shoulder), B to B(sleeve to sleeve hole), C to C (back to back), and D to D (front side to back side). The order is important, with the exception of C, which can be sewn together at any time.
Don't forget piping anywhere that there is a green line!
And this is what the coat should look like at this point!
With the exception of the frightening head, of course.
You will still have to add a hood, which can be best done by patterning one off of an existing hood you might have lying around.
I give a general example of a hood pattern here:
Don't forget there is also a double seam on the edge of the hood! ^.^
Good luck, and I hope this helps!