Can you make a Maplestory private server and not be sewed

The official answer is that you cannot, as it is illegal to do so and a rather serious offence violating copyright and intellectual property rights.
A private server requires you to have other users, however if you were to host a private server for just yourself it would not be detected by Nexon. That is the only way not to get sued by Nexon, and even then it is morally wrong. Just play the game they made.