Get a non-offensively coloured biro, pencil is tricky to see on suede. Use tailor's chalk if you have any. Find the straightest edge of your hide and draw a long straight line. Make sure it doesn't bend or you'll have a nightmare sewing them on straight. Lay the straight edge of your template on the line and draw around it, all the way to the end. Do your next row of scales so that the pointy bits tessalate into the spaces left by the first row. Fill your hide with rows of scales. Make sure you draw single scales in any little areas that are too small for a row, you'll need single ones as well.

Cut out all your rows of scales. You can now draw equally spaced lines on your tabard for where you want all the rows to go, but as the leather might slip around as you sew it on, you're as well to do it by eye, but make sure that the lines stay horizontal as you move up the tabard. Starting at the bottom, sew a row of scales on, so the scales come over the bottom edge of the tabard. Trim off when you get to the end, making sure you keep any half-scales as you'll need them later. Place your next row over the first row, so that the tips of the scales just cover the join of the scales in the first row, and sew on, covering the stitching of the first row. Try to stop the leather slipping around as otherwise the scales may end up not fitting perfectly with the first row. This is bound to happen eventually and is frustrating, but fear not, you can fix the problem by cutting the row and either slightly lengthening or shortening the distance between scales to correct any slippage introduced by the sewing machine. Fill in the ends with half scales - obviously each alternate row will have to end on a half-scale for the pattern to interlock.

Do this, all the way to the top. With odd scales, or more rows, you can neaten up the neck hole and shoulders in whatever manner pleases you. When you're finished, to make the half-scales sit flat, I'd run a row of stitching down each vertical edge. This stitching will be visible but it keeps the half-scales sitting neatly.