Maps 18,19,20,and 21 are missing

Should I make those levels or let you make them? I'm trying to make them now.

Well, you are welcome to make it, but I doubt it will be in the official Srb2.exe

The level designers will make them when they get around to doing so, they are probably working on some of them right now. Besides the team working on the game have to work on bugfixes to make the game playable and they have their own lives as well.

Just be patient, it will be done when it is done.