We will use the NC Double Buttress as the example here.  Gather these parts first.  

Note: The single buttress parts will be shorter and will only use one of the “U” brackets per buttress.

Glue together the stack of pieces to make the core as shown here and glue them into the back plate.

Glue the “U” bracket/s onto the front slot/s as shown

Glue hook rails into the slots on the outside edges of the bracket making sure the engraved detail is facing out.