Due to different sizes and needs to make your own custom coat, I'm sharing the ways I altered a purchased sewing pattern to fit my own needs and tips in construction that I prefer to the pattern steps. Basically, the pattern calls for hand-stitched hems and I skip that and use a few tricks to do as much as I can on the machine for a quicker, stronger seam because I detest hand sewing and avoid it whenever possible.
I used McCalls 5525 as my base pattern for this coat.
I knew I was lining it with fleece which is thicker than regular lining, so I started off by cutting out 1 size larger than my measurements to make room for the thick lining.
I also have broad shoulders for a chick, so when I cut out my coat, I taper my cut lines to the next size up for each line/piece above the chest. You just have to make sure you're consistent on all the pieces, tapering out for the front, back, lining, etc to ensure all shoulder seams align. Collar would also be the size up.
1. Lengthening/ Shortening Sleeves
Whether your making a short sleeve into a full length sleeve, or in my case, adding 3 inches to a long sleeve pattern, the principle is the same. You keep the curve of the the pattern at the shoulder which was designed to fit into the body of the coat, and add or remove length in the body of the sleeve.
black garments make for terrible tutorial photos, thus the sketches for the following tips
2. Assemble Coat Exterior to Lining
I use the same steps to create the outer coat and lining. Basically you're making two of the same coat, the lining is just 1" shorter and has the outer (black fabric) for the center front panels. So you just sew all the seams around, add the sleeves, add collar to exterior, etc for both sets.
But where I deviate from pattern instructions is attaching them together. I always sew as much as I can with my machine.
You'll place the exterior inside out and insert the right side out lining into it, so they are layered right sides together. You'll trim the corners and all the seam allowances, then pull the whole coat through your hole, making just a few inches to hand sew, rather then the whole back of the coat.
3. Hemming Sleeves
Most sewing patterns I've purchased also just have you hand sew the sleeve hems when using lining. You most often never want machine top stitching showing on a wrist hem of a blazer or dress coat, so it makes sense. But what a pain. I machine sew invisible hems for my sleeves due to my hatred of hand sewing and the fact machine sewing is cleaner and stronger than my hand sewing.
You'll first try on your coat to mark where your sleeve should hit. I add 2" to the mark of the exterior for the fold and seam allowance. The lining, however needs to be shorter as the exterior folds up inside to meet the lining seam. So cut your exterior sleeve ends first. Then pull your lining down and I leave the lining 1.5" shorter than the exterior.
You'll also leave or unpick a hole in one of the lining sleeve seams.
The following diagram is how you access the sleeve hem, by going through the center of the coat between the lining and exterior, and will pull it out the sleeve hole, sew the hem, then jam it back through the middle of the coat to create a perfect finished hem.
Once you've fished through the coat and pinched the sleeve ends which are folded to be right sides together, you'll pull them out your sleeve hole, but how to sew them together?
Pin the sleeve seams together and you make them kiss basically, sewing around the circle on the wrong side of the fabrics, with right sides together as sketched below.
You're lining is shorter, so when you put the sleeve back through the coat and down where it should be, you'll have a great looking finished hem, all inside the coat, and you can press the end to make the crisp folded edge on the exterior.
To hem other side you'll repeat the same way, and it's easier since you just pull it out of the same sleeve hole rather than fishing across the whole coat.
To finish the hole in your sleeve lining, I just fold raw edges under and top-stitch it closed, as no one will ever see it.
Thanks and good luck adjusting a pattern to make your own pea coat!