Перестать делать means that you were doing something and you have stopped doing it but you haven't completed it
Закончить делать means that you have finished doing something w/o specifying if you actually completed it or not (but in majority of situations it means that you completed whatever you were doing)
Сделать means you've done it completely
Доделать means you were doing something then you had a pause in doing that something (by any reason) or you were in the middle of doing something and now you completed what you were doing