To make an add-on, (Except for prints, maps, and perhaps a few other simple types), you must first learn how to write scripts. Blockland is a game engine, and then a massive pile of scripts that tells it how to be Blockland. To make an add-on, you must learn how to create scripts that teach the game engine how to do what you want it to do. Generally, people start with a new gun, and that is fairly simple because you are editing datablocks mostly, rather than actually writing scripts.
Start by learning how to open, edit, and create .cs files (renamed .txt files used by the torque engines, not C# source files, although they both have the same file extension), and then work through a torquescript tutorial or two. Once you feel you know something, try reading someone else's script, and try to understand how it works.
It would take months for a genius, or years for a dedicated average user, to reach the point where they could create their own duplicator, longer if they want to make it run faster than the one on RTB, but with time and effort, anyone should be able to reach the point where they can have a 3d maze generator that loads cavernous chunks from files to use as the cells of the maze, that can tolerate one-way passages and powerups to create a metroidvania adventure where you cannot get yourself stuck, but success is still a fun challenge.
However, if you ever give in, and become another one of those people who say "maek me adonn!", you won't get anywhere, because few people want to make something for someone else, and then give it away for free. People do sometimes work with other people, especially where one person is an exceptional modeller and the other is a talented scripter, but nobody will make a complete add-on for free and then give it to someone else to claim all of the work as their own.
Good luck, happy learning, and hopefully, if you at least try, we will see some of your work on RTB in a few months, and not in the fail bin!
