Gather these parts
Glue the two outer walls into the backer plate
Glue the top and bottom plates on as shown.
Gather the ruins inserts
Glue the ruin inserts into the holes on the inside of the construct
Glue the buttress strips in place on each side
You’re all done!
Prime with Rust-o-leum Profesional Enamel flat black and paint as normal with hobby paints.