Door props are simple devices -- simple as a wooden wedge that sits on the floor. When you tuck the narrow end of the wedge under a door, its shape prevents the door from moving forward. So, use a door prop to keep a door open or tuck it under a closed door to help keep it shut. Also because of its simple shape, a door prop is easy to create. Build your own door prop in less than 30 minutes.
Draw a line that wraps around your wooden block. It must be straight and the same distance from the end of the block on every side.
Measure the intended size of your door prop down the block from that line. Though sizes may vary -- the length of the door prop affects its angle -- try making your door prop between 6 and 8 inches long. Draw another line that wraps around the block at this distance.
On one side of your wooden block, draw a diagonal line that runs from the top of one line to the bottom of the other line. Cut the block along this line using a band saw, then cut along the two parallel lines; what remains is the basic shape of your door prop.
Sand the edges that you cut with sandpaper, being careful not to sand so hard as to compromise the door prop's sharp edges. You may sand the pointed end of the wedge, as well, so that it is not as thin, sharp and liable to break.