Is this what you're talking about?
http://www.cantho-rvn.org/craft/waddell-21-550x374.jpgIf so, I'd start with sheet styrene for the base and thin strips of styrene by evergreen. You can get the large and thin strips pre cut to thickness. You just cut it to size.
They also sell styrene in 'corregated' form, stuff that looks like the corregated metal.
Let me know if this is what type of revetment you mean and I can add more detail.
Found this too
http://www.wpafb.af.mil/museum/history/vietnam/revet.htmId definitely look into a styrene solution. Evergreen makes a bunch of prefabricated styles, cobblestone, corrigated, brick, etc. I'd check them out. I'm pretty sure they come in different scales.
If you can't get the prefab stuff, you could scribe your oun from a blank sheet. Just use the back of a #11 blade and a ruler. Scribe in the recesses. Use stock strips for the vertical pieces. The base could be poured plaster. Make a simple block mold out of small strips of styrene glued with epoxy. Get some woodland scenic plaster or regular plaster of paris or household spackle. Fill the mold, let it dry, pop it out, clean it up.
thats a start - ask more questions as you go.