Pretty easy project. I cut a solid door in half lengthways and then cut the length down to about 57 inches.
Step 1: Cutting Spacers and Seat
I cut 4 inch strips off the sides of 2 hollow core doors the same length. Then made 10 spacers out of old wood shelving. Then just started gluing and stacking.
Step 2: Last Step
After glue set I would pre-drill and fasten them together. Door/slat to spacer, repeat till I got to the solid end piece. Then I ran one long wood screw the entire width.