Working with aluminum is problematic. I bought it at Home Depot where it is sold as flashing. It is very thin, so I can easily cut it with an ordinary scissors. They have heavier aluminum and tin that you need a tin snips for, but that would be too hard to work with in this context. The leather I bought at a craft store. It comes in every color and is beautiful to work with.
As with all my abstracts, I don't know what it will look like when I start out arranging the different materials - that's the fun of it!