reinvent the wheel

reinvent the wheel v.  To design or implement a tool
   equivalent to an existing one or part of one, with the implication
   that doing so is silly or a waste of time.  This is often a valid
   criticism.  On the other hand, automobiles don't use wooden
   rollers, and some kinds of wheel have to be reinvented many times
   before you get them right.  On the third hand, people reinventing
   the wheel do tend to come up with the moral equivalent of a
   trapezoid with an offset axle.