Now you can tape down your pattern onto the smooth side of your leather. This is the time to think about which way you intend the sheath to be worn - either on one’s right side or one’s left, and be sure to lay your pattern on the leather with this in mind. Unless specially requested otherwise, I make all my sheaths to be worn on the right side, with the cutting edge of the knife facing the rear (this is how I prefer, as a right hander, to wear my knife).
Also be aware that since leather is a natural material, even the best quality stuff will probably have some small (or large) marks or defects on it, some of which you may want to work around so as not to spoil the beauty of your finished work of art.
Carefully trace around the pattern onto the leather with a pencil. If you intend to use your pattern more than once or twice, it might be worth making a more durable pattern. I like to use clear lexan of about 1/8” thickness. This is stiff enough that I can simply hold it down onto the leather with one hand, and easily trace around it. Also, since it is clear, I can see through it to the leather’s surface to verify that it is defect free.
I like to lightly mark a center line on the leather where the fold will be. This will help later when lining up the belt loop for stitching, and also if I want to lay out for decorative stamping.