I thought I would just quickly share with you this 1812 Tailcoat Pattern. You can find it in the pattern section of Wm. Booth, Draper. The pattern actually has a wider date range on it than strictly 1812: it is listed as a tailcoat pattern 1800-1820. This is the description:
This tailcoat pattern is the first well made civilian tailcoat pattern specific to the first two decades of the 19th century. The pattern comes with three sizes: Medium, Large and XLarge. There are two options for the collar, comprehensive directions and documentation.
And here is the information about the quantity of fabric needed, etc. (the underlined sections are other items that Wm. Booth, Draper carries):
To make this coat between 2 1/2 to 2 3/4 yards of superfine wool broadcloth or slightly more (to allow for shrinking) linen and about the same amount for a lining of oatmeal 3.7 oz. linen is required. An extra 1/4 yard will be needed for the pocket bags. Notions needed are about 1 1/4 yard linen buckram interfacing, between 6 to 8 5/8″ buttons or button molds, one or two additional buttons that are flat on both top and bottom are recommended for a double breasted coat. For the sleeves 4 to 6 1/2″ optional matching cuff buttons or button molds are needed as is Linen threadof either 50/3 or 35/2 to match the lining and outer fabric. For sewing the button holes you will need one or possibly two spools of quilter’s thread or buttonhole twist that matches the outer fabric.