To breed common plecos you need a pond in a tropical enviroment like south Texas and central to south Florida. The males dig caves in the banks of the pond. This behavior seem to be needed for commons and is next to impossible to duplicate in the home aquarium.
If you wish to breed plecos, I suggest you start out with Bristle nose and move up to any of the hypancistrus species, particularly L260 is a simple to breed pleco.
When you move from BNs to more difficult species be sure to follow the guidelines I outline in the breeding plecos thread at the top of this forum.