A) Sides: Take one 24"x6' glued up board. Starting on a center 36" up one edge,draw a 12" Radius arc toward the middle of the board. Starting in the exact center of the board, (36" up, 12" over) Draw another arc extending the previous one in an 'S' curve toward the centerline. Extend this in a straight 6" line toward the far side of the board. Starting on a center 24"' up on the opposite side, and 6" in, draw the final arc from the 6" extension down to the edge of the board. Duplicate this line from the other end of the board, flipping it top-top bottom, and left-to right. Cut the results out with a fine-tooth saber, scroll, or band-saw.
B) Feet: Starting on a center 6" in from the sides, along the bottom edge, draw a 6"-radius arc. On the long front and back, draw complementary arcs 6" on either side of the centerline. On the shorter sides, draw the complementary arcs from the other side of the board. COnnect the top of the arcs with a straight horizontal line, 3" in from the edge. Cut these out with your scroll-saw.
C) Front/Rear panels: front and back panels are mirror Images, constructed identically. Glue/screw a 6' 1x2 along the entire top inside edge of the panel. Cut a 22.5" 1x2 to fit down the left and right edge, to the floor. Cut a 4.5" peice of 1x6, and attach that centered in the middle-foot, with the grain running crosswise to the panel. Finally, fit two 31.75" 1x2s between the center-foot-block, and the edges.
D) Side panels: The boxing-in parts of the side-panels fit inside the one for the front and back panels, and therefore are set 3/4" in from the front and back edges. Run a 22.5" 1x2 across so the top of it is 24" above the floor, centered 3/4" from each edge. Running down from each end of that, put another 22.5" 1x2, ending at floor level in the foot area. Cut a 21" 1x2 to go across at the bottom, between those. Screw/glue from the inside.
E) Box Assembly panels: Assemble the front, sides, and back, by screwing from the outside, through into the 1x2s attached to the front and back.
F) Back Support: The smaller 18"x24" glued-up board should just fit between the rising part of the arms/sides. Since there's noplace to put a 1x2, pre-drill, and carefully screw the side-peices to the endgrain of the back support. Then cut some 1x4s to screw upright to the back for additional support
G) Seat Support: Drop the remaining 24"x72" glued-up board, into place as the seat, and screw a 4' piano-hinge in the where it meets the back rest. You may, depending on who's going to be using the settle, find that you need to screw reinforcement boards crosswise inside the seat.
H) Inside Bottom: Cut a 22"x71' peice of wood out of plywood, masonite, or whatever else you've got around, cut 2.5"x2.5" notches out of the corners, and work it diagonally into the box, and then straighten it out and force it into place. It will be a little loose. If this bothers you, glue it into place.
Paint and/or carve to suit.