Cardboard box with very light reinforcing. The neck is birch veneer and the box reinforcing is really light pine or something like that--all the wood came from a pallet made in Europe. The lid is held on with four tiny screws.
Front. The grommets were made for tarps--the lid is almost too thick; next time I'll glue them on. Fret Distances Calculator is from http://www.buildyourguitar.com/resources/fretcalc/index.htm The "frets" are only pencil marks. The neck is 15/16 inch wide, rounded in back, about 1/2 inch thick, and cut away under the box lid (this section was later reinforced). The small sizes were chosen because this was intended as a gift for a child with small hands. I recommended that it be restrung with nylon strings and that presently it sounds best when played like a lap steel guitar.
This picture is in poor focus but you can see two brass strips that the strings cross at the tail: these are L-shaped in cross section and I bought 36 inch pieces that way but they could easily be bent from thin metal; they are glued with super glue; the shorter one sits in a fret slot. They should prevent cutting into the wood and cardboard.
The nut is a wire tie; I don't have any idea how long that will last. The bridge is a small bolt (intended for light fixtures) for low action and less finger pressure.