Steps

1. Gather your materials (see "Things You'll Need" below). All of the materials are inexpensive and can be picked up at your local builders supply store.
2. 

   Figure 1: The template for the footprint of the coffin. Angles 1 and 2 are 49 degrees each. Angle 3 is 80 degrees. Angle 4 is 76 degrees, and angles 5 and 6 are each 53 degrees. Click on image to enlarge.
   Create your template. Use shelf paper or some other large sheets of paper (the plain white back of gift wrap can work if you're on a budget), and tape the pieces together so that you have one sheet that is large enough to hold the design for the "footprint" of the coffin. Note that this is not the template for the base, which will be slightly smaller, but rather it is the template for the coffin with the side panels secured to the outside edges of the base. This template allows you to obtain the correct measurements for the sides of the coffin and the correct angles at which to cut the sides. See figure 1 for the dimensions of the coffin. Use a t-square or carpenter's square, and first draw the two perpendicular lines in the middle. Then draw the top and bottom edges, and finally connect the endpoints of the lines to form the sides as shown.
3. Cut the sides of the coffin. The sides of the coffin will be 1' high, so take one of the 4' X 8' plywood panels and cut it lengthwise into four 1' X 8' pieces (you'll need three of these to make the sides). Use a circular saw to cut the side panels according to the dimensions in figure 1. Make sure to cut the side edges of the panels at the correct angles so that they will fit together. For example, the panel at the "head" of the coffin should be 24" (2') wide, and the edges should be cut at 53 degree angles.
4. 

   Figure 2: The template for the base of the coffin.
   Draw a template for the base of the coffin. The side panels will be nailed to the outside edges of the base, so the base is slightly smaller (3/4" smaller on each side, assuming you are using 3/4" thick plywood) than the overall footprint you drew before. Tape sheets of shelf paper together as you did in step 2, and draw the base--once again drawing the two perpendicular lines first--according to the dimensions in figure 2.
5. 

   Figure 3: The base and sides pieces of the coffin.
   Cut the base of the coffin. Clamp your paper template over the remaining 4' X 8' sheet of plywood, so that the vertex of the widest point of the coffin touches the edge. Use your circular saw to cut out the base of the coffin around the template.
6. Cut the lid of the coffin (optional). Use this step only if you want a top for the coffin. Place the base over what is left of the 4' X 8' sheet of plywood so that it fits entirely on top of the wood. Trace around the edges, and then remove the base. Cut out the top of the coffin following the lines you traced.
7. Assemble the coffin. Now it's time to put it all together.
   
   
   • Dry fit the sides of the coffin together and to the base. You just want to make sure that everything will fit together correctly before you start gluing the pieces.
   • Glue or screw the side panels to the base and to each other. The bottom edge of each side panel should be flush with the bottom of the base. Drive 1 5/8" screws through the side panels and into the base, and use glue, screws, or biscuits to secure the side edges of the panels together.
8. Finish the coffin. If there are any holes or dents in your plywood, fill them with wood plugs or filler. Then stain the wood or paint it as desired. You can be as creative as you like in your decorations. If you wish to line the inside of the coffin with drapery or other fabric, you needn't worry about staining the inside. Simply glue or staple the fabric to the inside.
9. Attach the lid of the coffin. If you're using the coffin for burial purposes, you can just nail the lid on. Otherwise, attach a piano hinge to one of the long edges of the coffin, and attach the hinge to the lid.

Tips

• Plywood is fine for a holiday prop, but if you want to make a coffin for "graver" purposes, you'll probably want to make it out of real wood. A wide variety of woods have been used in coffin-making, including pine, oak, and cedar.
• This design can be enlarged (for a plus-size coffin) or made smaller (for a pet coffin, for instance) by scaling it up or down. As long as the dimensions are kept in proportion, the angles will remain the same.
• Countersink all screw holes for added strength.
• When cutting the wood, make sure to account for the blade when setting your guide. For example, to cut the 12" wide strips, you will probably want to set the guide at 12 1/8".
• This coffin can easily be made into a bookcase with the addition of shelves. See the source page listed below for specific instructions.
• If you hide inside it (cushion it) and open the lid and sit up when you hear someone coming, it'll freak 'em out.
• Dress up as a vampire when doing so.
• You can sprinkle flour and debris over the coffin to give it an ancient appearance, and throw in some fake cobwebs to make it look extra scary.
  

  Sprinkle flour and debris on coffin to make it look old

Warnings

• Exercise caution when using a saw or other power tools. Follow the manufacturer's instructions, and heed all warnings.
• Apply stain, varnish, or paint only in a well-ventilated area. Follow the manufacturer's instructions and warnings.

 Things You'll Need

• Two 4' X 8' sheets of 3/4" plywood (or other suitable wood as desired)
• Circular saw
• Wood glue and 1 5/8" screws
• Shelf paper or other large sheets of paper
• 48" piano hinge if an opening lid is desired
• Wood plugs and/or wood filler
• Fabric or drapery (optional)
• Wood stain or paint