Start with the bottom. Cut and fit all pieces before adding glue. If the cedar is tongue and groove, you will only have to fit at the ends. If the board is thin, you can cut with a sharp utility knife and then plane the edge. Otherwise, a fine-toothed handsaw is recommended for the crosscuts and a rip saw can be used if a lengthwise cut is needed.
Glue the boards to the bottom of the trunk and let dry. Make sure they fit tight together lengthwise but there can be some leeway at the ends, because side boards will be placed on top.
Cut the pieces for the two ends of the trunk. You have a choice of running these boards in either a vertical or horizontal direction. Most woodworkers will probably opt for running all boards in a horizontal direction. If this is the case, work from the bottom up. The rip cut on the last board is very easy to mark. Once this board is in place, make the mark from the outside with a carpenter's pencil. Then make the cut with a very sharp utility knife or a sharp rip saw.
Glue the end pieces into place.
Measure and cut the boards to go on the two longer sides. This is done in the same manner as Step 3. Check the angle with a speed square and then make a mark on each end of the board using the speed square to transfer the angle. Mark the top board again by running the pencil across the top of the side of the trunk and cut with a knife or rip saw.
Glue these side pieces and let the glue dry. With cedar there is no need to add a finish.