A drill to drill screw holes and rope holes, and to drive screws.
1/8" drill bit (for pilot holes for the screws)
1/2" drill bit (for the rope handle holes)
Screw driver bit
With these instructions and materials, you can make a coffin up to about (inside measurements) 79" (6'7") x 31" x 16". In my experience, a coffin should be 4" to 6" longer than the person is tall. Interior width and depth are usually 22" wide and 12" deep, but you'll have the material to make it the size you want. Measure the width and depth of the person while they are lying down. If the person will be buried in a conventional cemetery, the coffin should be a maximum of 29" wide outside, because the cemetery usually requires a grave liner or a vault, which will be only 30" wide. (Green cemeteries do not allow vaults.) Call to check their regulations.
If you don't have a table saw, or a friend who owns one, you can still make this coffin easily. About half the lumberyards in my area plus Home Depot and Lowe's will cut the plywood for you, for a reasonable fee. Call and ask.
IL = Interior length
IW = Interior width
IH = Interior height
The top of the coffin will be attached by driving screws through the ends into the cleat on the underside of the top.
When cutting the rope, wrap masking tape around the rope at the point of the cut, then cut through the middle of the tape. This keeps the rope from unraveling and makes it easy to pass the rope through the holes. Tie an overhand knot in one end of the rope, pass it out through one hole and in through the other, then tie another overhand knot on the inside.
Sand anything that looks to you like it should be sanded, and finish it in any way you choose. I like to put a coat of shellac on my coffins. It gives the wood a richer look, and it prepares the surface for staining or painting. Consider encouraging the family and friends to decorate the coffin. Jerri Lyons, a home funerals pioneer, calls decorating the coffin "a healing act of art therapy."
If you want your coffin to look a little classier, add one inch to the length and width of the top and bottom pieces. This will allow the top and bottom to overhang the sides and ends by 1/2", which means you don't have to get every edge precisely flush.