That is always a thought that they'd make something from the skin seeing as they do use bones to create frames for weapons or decorate them, but isn't Human leather not particularly great?
You only have so much area on a Human and isn't the strength of it not as good as it could be? I was pretty sure that besides ethical reasons we don't do that because it's not a particularly great product. I could very easily be wrong of course, but I also don't think there's any evidence either to suggest they use the skin of Humans for anything. It's implied they'll use the skin for something seeing as Jungle Hunter does wear a little leather and Scar does know how to fashion makeshift armor and weapons, but I don't believe in the films either they've collected Human skin for anything. Skulls sure, but Human leather I'm not too sure.