I made this coat to be the Beast for Halloween. I looked around online, but it was difficult to find a pattern for the style that I liked. So I drafted this from a pattern contained in the History of Costuming book. It was then sew together with lining and trim.

Step 1: Drafting the Coat: Supplies

Supplies:

Pencils
Tracing paper (I find that medical exam paper is cheap and works great: http://www.amazon.com/Medical-Pattern-Paper-Patternmaking-Drafting/dp/B007AH74VO)
Hip and French curve
Meter stick (or yard stick that shows cm)
Measuring Tape

I drafted this from a pattern contained in the History of Costuming book: https://archive.org/details/historyofcostume00khle (see figure 438). You will see numbers on the pattern drawing. These numbers indicate a distance in cm.

Step 2: Drafting the Coat: Get Your Measurements

We want to make sure the coat fits you correctly, so make sure you get some proper measurements done. For reference: http://www.madalynne.com/how-to-draft-a-block-pattern-part-2
For this coat what you will want will include:

Bust
Waist
Neck
Armscye (around the arm where the armhole is)
Back width
Shoulder width
Neck-to-waist
Arm length
Elbow Length
Wrist
Bicep

Step 3: Drafting the Coat: Drawing the Back and Front Pieces

So here is where things get fun. I started by drafting the back of the coat. Draw the center line and make it as long as you would like the coat to go (I measured from the neck to about my knees). I based a lot of my drawing off of the measurements that were already there. I found that many of them already matched me. I did needed to widen the back to match my back width (marked 'B' in the picture), as well as lengthen the shoulders (A). The tails should start somewhere around the natural waist line, but can go a little above the waist if that's the style you prefer. Also, be sure to add a couple cm of easing to the back width measurement. These coats are meant to fit fairly tightly across the back (to push your chest out), but you still probably want to move a little. I could go more into costume drafting, but that is entirely it's own subject and I'm sure you can Google plenty of useful resources to help.

After drafting the back, I drafted the front of the coat. Make sure that your shoulder lengths match. It would be sad if they didn't. Also, use your different curves and measuring tapes to ensure that the side seams match as well. I then found that I had to greatly widen the armhole for me. So use your armscye measurements to try and get the hole to be the right size for you.

Once you have finished drafting, be sure to add in a seam allowance. I added in 5/8" (I know, I changed units, but that is the seam allowance I'm used to, so deal with it).

Note: When I draft, I prefer to err on the large side of things. It is a lot easier to take in an outfit than widen it.

Step 4: Drafting the Coat: Start Your Mockup

I strongly suggest making a mockup whenever you are drafting a pattern. It makes things so much better.

Supplies:

Basic sewing supplies
Cheap fabric

So I just found some really cheap broadcloth on sale to use for the mockup. I started it now before adding the sleeves and collar. I wanted to make sure I was satisfied with the look of the body before going through the trouble of drafting sleeves.

Cut out two back and two front pieces. Attach the back pieces down the center up to the tails. Let the tail pieces overlap each other. Then attach the back to the front pieces. Start by attaching the shoulders, than the sides.

Try on the mockup and test the fit. Have a friend/relative/etc help you size things up. Mark the modifications that you need to make on the mockup. Once you are satisfied, transfer the changes to the pattern. Note that this style of coat is not designed to button up.

Step 5: Drafting the Coat: Making the Sleeves

The sleeves can be a little tricky. Make sure that you measure things well. You will want to measure around you hands to make sure that they fit through your cuffs well. Also, on a curved sleeve like this, it is very important that you get the elbow in the right spot, or the attached sleeve will look very awkward. I actually straightened out the sleeve a lot on mine.

What also may help is to find a similar looking sleeve from another pattern. Trace it and fit it. use your armscye and bicep measurements to help you here. Add in your seam allowance.

Cut out a mockup of the sleeve and try attaching it. You only need one sleeve for the mockup. Note that this process may require a few iterations. It took me at least three tries to make the sleeve look right. Then it took me a few more tries to get the sleeve positioned on the coat in a way that I liked. Try comparing to a suit coat that you know already fits you nicely.

If you need help attaching a sleeve: https://www.google.com/search?q=how to attach sleeve

Step 6: Drafting the Coat: the Cuff and Collar

The cuff and collar are easy to draft after you have the main part of the coat complete.

The Cuff
The cuff is drafted by measuring the bottom of the sleeve pattern. Draw a line matching that length. Then create a trapazoid buy drawing another line 4" (about 10cm) above the first line adding an inch to it.

The Collar
The collar is made by creating a rectangle. Measure the mockup going from coat front edge to the other. Go up about 3 inches (all depending on how high you want the collar).

Try these on the mockup and see what you think.

Once you are satisfied with the mockup, it's time to get fabric and make the coat.

Step 7: Making the Coat: Materials

Materials is entirely up to personal taste. I made mine from a nice silky looking fabric with a flower pattern. Other coats may be made from velvets (avoid the stretch stuff) or even your home furnishing fabrics. You will probably want a lining as well. This can be made from your choice of normal lining materials or broadcloth.

Supplies:

Main fabric (about 3-4 yrds). Remember that it is always better to err on the side of too much.
Lining fabric (about 3-4 yrds)
Trimming (about 4.5 yrds) Measure your costume to make sure
12 front buttons (optional)
2 back buttons (optional)

Step 8: Making the Coat: Cut Out the Pattern

Fold the fabric in half and lay out you patterns. You will need to cut out all of the pieces from the main fabric. Also, the cuffs and collar will be the main fabric on both sides. Make sure to cut out enough cuff pieces for both arms.

From the lining, you will need to cut out the main coat front and back as well as the sleeves.

Step 9: Making the Coat: Sewing the Main Part

Sew the backs together (with right sides together) going down to the tails. Then attach the front pieces in the same way you made the mockup. Do this for both the lining and the main coat.

With right sides together, pin the lining to the main coat. sew down the front parts going from the collar to the bottom of the coat. Now would be the time to turn the coat with the right sides out and attach the trim that goes along the front. make sure that the trimming matches on both sides.

Once the trimming is attached, flip the coat inside out again and sew along the bottom. Go up the tails and make sure the lining attaches to the main coat correctly. Don't sew around the arm holes and neck.

Flip the coat right side out. Baste around the armholes and neck now. Iron everything so that it looks nice.

Step 10: Making the Coat: Sewing the Sleeve

Attach the two parts of the sleeve for both the lining and the outside. Iron open the seams, and flip the outsides of the sleeve right side out.

Sew together the cuffs. This is done by sewing together the sides, then attach them at the top. Before you close the loop, attach the trimming to the outside. Close the loop, turn the cuff how it needs to go and iron.

Pin the raw edge of the cuff to the bottom raw edge of the outside sleeve and baste them together. Take the lining (still inside-out) and lay over the sleeve and the cuff (you should see the wrong side of the lining outside of everything). Match up the bottom raw edge and attach. Trim the seam allowances and pull the lining inside the sleeve. This will nicely cleanup the cuff of the sleeve. Iron the sleeve and add ease stitching to the armhole side of the sleeves.

Step 11: Making the Coat: Attach the Sleeves

Once the sleeves are done, pin them to the main coat. Pull in the easing (keeping things nice and even) and baste on the sleeve. Once you are satisfied with the attachments, sew them in. Cleanup the raw edge (serger or other means).

Step 12: Making the Coat: Make the Collar

Take some stiff interfacing and add any trimming. Attach it to the wrong side (inside) of the outside collar piece. Pin the bottom of the outside collar piece (with right sides together) to the neck line of the main coat. Stitch in place. You will have the seam allowances hanging off the side. Iron the collar and neck upward.

With the inner collar piece (the side touching your neck), iron up the bottom part to the seam allowance (ironed up side is on the inside). With right sides together attach the outside and inside collar pieces by stitching up the sides and along the top. Make sure you line up the seam to the front of the coat. Trim the seam and corners and flip the collar right-sides out. Stitch in the ditch around the collar to attach the bottom of the inside collar piece. Iron.

Step 13: Making the Coat: Finishing Touches

Now is the time to touch everything up. Clean up you stitching, iron and sew on your buttons. There will be about 12 buttons that go down the front (unless you decide to go down both sides), and 2 buttons in the back.

Now your coat is complete. Go out and enjoy!

For the costume I'm wearing it with:
- Breeches and shirt are from Simplicity 4923
- The vest is just made from your favorite vest pattern
- The Jabot is just layers of gathered lace on a square of fabric. This was then attached to a neck strap