I have a knife block full of medium grade stainless steel knives for general use, but I also have a high quality forged cook's knife I keep separate. The duct taped cardboard it came in was okay for a while, but I wanted to make a proper sheath for it. I decided to make a wooden sheath, sort of a one knife block. It's a pretty simple build and I've very happy with the end product.
Step 1: Cutting the wood
I started with a 1/2" x 4" poplar board. You can use whatever hardwood you want, but in the big box stores around here you get poplar or red oak. Place the knife on the board and mark down 1/4" on either side plus a little buffer. Cut two pieces of wood to the marked dimensions. I wanted a bit of a thinner sheath so I planned one block down to 1/2" thick.