Mark, there are a lot of certified paid service providers here that have the very knife or a real pattern that could make you a better fitting sheath IMHO than someone using a sketch.
Next, if your friend is not a blade forums supporting sheath maker it would not be proper etiquette to assist him in making a sale.
Also, not that this is your intention at all so please do not get offended, but as a precaution to avoid knock offs or counter fits a tracing could potentially lead to problems.
Sorry, to seem anal to anyone but the post was reported and sadly today knock-offs are becoming a thorn in everyones side.