I believe this armor is made of cloth and fiberglassed cloth scales and lames. I think the only actual leather is the brown shoulder straps. If you're looking to create armor like this for SCA or larp, you should check with the particular organization as they have their own guidelines (leather must be 10 or 12oz or 13-15oz, etc)
If you're going for a costume and need no real physical protection, you could probably use 4-6oz or 6-8oz leather.