I had thought about using sheet metal. What would really be nice is paneling with some sort of texture. I could experiment with wrinkle finish paint, but since we try to make our airplane restorations great looking on the outside, I figure to try and make something simple but attractive on the inside.
I looked a decorative aluminum sheet at the home improvement stores. Patterns aren't great and the sheets are to small. I have used ABS plastic sheet on other projects. Easy to form, texture, fire resistant, relatively inexpensive, but a bit on the heavy side.
I did find corrugated plastic sheet. Textured, easy to form, very light, inexpensive, but fire resistance and durability in question. Can't find any data on it's flame resistance. My own burn tests shows it burns slowly and drips flaming droplets. A search of CAR4a regulations doesn't show any requirements for flame retardant interior materials.
Photos attached.