Read (or reread) plus-readme.txt. After that, look at a jailbreak level that works (I recommend looking at the example that comes with JJ2+) and then try to build a JB level yourself, by copying what the example does. Try to make your copy as close as possible... thus, use the same events, the same trigger ids, etc. Once you get that working, start experimenting. After you get a good feel of that, then you can make a full JB level.