Recommend novel that MC self-create skill and technique which he keep on polishing its flaw until he reach the summit. like: Immortal Mortal Stellar Transformation more or less: Lord Xueying
Stellar Transformation has a thing where the MC inherits someone's special unfinished self-created skill which he ends up polishing to the absolute summit.
The Legendary Moonlight Sculptor then! This has a skill that is considered weak by everybody that the MC inherits which he takes to new heights by unlocking every secret that the skill holds!
The strongest system - he keeps leveling the skills and evolves them continously. He doesn't self create tho
The Book Eating Magician developed his own ultimate skill and improved it. Before that he takes skills and tweaks how they are usually applied for the best effects