Hi Angela,
If you had ever seen one in use, you wouldn't want to build or use one. You start with a 6' length of 1" iron rod. Make two 90° bends on one end to form a crank. Sharpen the other end.
To keep the spit from spinning loosely in the hog, you must build 2 gadgets which are clamped to the spit and have two sharp arms to stick into the hog.
Make two support posts by welding a "V" on one end of a 2" iron pipe, 5" long. Drive the pipes into the ground 2' so that 3' is left above ground.
Actually, hogs cook just as well laying still and quiet.
Have fun,
Smoky