reinventing the wheel 

Starting something over completely from scratch when there is already something prepared. Often done unnecessarily and for the purpose of taking full credit.

Michelle: Did you see the dress Jenny made? It's just like that one we saw at the mall, except the straps cross.

Carly: Why didn't she just alter that one? She's always reinventing the wheel.

reinventing the wheel by Zach Willard July 6, 2008