Hi! I'm new here. I'm also fairly new to the experience of creating my own RPG (played quite a few, made my own settings but always with out of the book d20). It iss something I've been wanting to do for a long time but I'm only now putting real work into creating my own system.
I'm trying to create a game loosely inspired by myers-briggs (I've tried to search for games along this idea but couldn't find any). Some general information:
It will boast sixteen main classes based on each of the types:
Teacher, Counselor, Champion, Healer, Fieldmarshal, Mastermind, Inventor, Architect, Supervisor, Inspector, Provider, Protector, Promoter, Crafter, Performer, and Composer.

Rather than choosing from one of these sixteen classes in the beginning, you first start out classless and distribute points across your four main stats and their substats in any way you want. The four stats:
Thinking (THI): Intelligence. Determines max MP, spell power, and number of languages you know.
Intuition (INT): Psychic/spiritual power. Determines initiative (you know the battle is coming so you are more prepared for it), spell power, and number of 'psychic languages' you know.
Sensing (SEN): Vision, hearing, etc. Determines accuracy (long range weapon damage) and dodge (if you can see it coming, you can dodge it.)
Feeling (FEE): Emotion, instinct. Determines max HP (how good do you feel?) and rage (close range damage).
(The average of Intuition and Sensing is you reflex save. The average of Thinking and Feeling is your will save.)

Starting at level two, you start working up your way up the Keirsey temperament sorter, gaining 'super-classes' along the way, and arriving at one of the sixteen classes at level eight.
Level 1: Classless (choose race and stuff though)
Level 2: Choose Martian (N) or Earthling (S) super-class. Martian (abstract) and Earthling (concrete) are also political parties in the setting I'm making.
Level 4: Cooperative or utilitarian? Martian= Idealist or Rational classes. Earthling= Guardian or Artisan classes.
Level 6: Directive or Informative?
Idealist= Mentor/Advocate.
Rational= Coordinator/Engineer.
Guardian= Administrator/Conservator
Artisan= Operator/Entertainer.
Level 8: Branch out into the main sixteen.

Now... heres where I get to my problem.
I'm trying to solidify the main sixteen classes, but first I need to determine what each of the superclasses should do.
I would like to ask you some questions.
What should "Abstract vs. Concrete" mean in game mechanics terms (if anything)?
What should "Cooperative vs. Utilitarian" mean in game terms?
What should "Directive vs. Informative" mean in game terms?
What should "Expressive vs. Reserved" mean in game terms?

I'm sorry if there is already an mbti rpg out there, I've tried looking for one but couldn't find it. Any help would be appreciated. Thanks guys. :)

This is a question that gets asked in response to first posts frequently around here, but I am wondering what you want you game to look like.  What are you trying to do?  What is the challenge the players are facing?  What is the feel you are trying for and what do you want people (or Martians *wink*) to get from the game? 

Hmmm... good question.
Well, first and foremost I want for players to have fun, but I know that doesn't really answer the question very well. :)
I know one goal for players would be to simply level up (my play group seems to like doing that. When I DM I try to have everybody level up at least once per session.) The incentive to level up in this game is to become a powerful mage called a Pathodyne.
At level 1 you start out essentially classless, or as a Peasant if you prefer. The first eight levels are essentially training levels that you ought to be able to get through in one afternoon.
At level two you gain your first superclass Martian or Earthling. In this setting however, Martian and Earthling don't refer to the planets in our solar system but to two political parties in the magical city of Logotopia. For one scenario I was planning to have players start out in line at the polling place when suddenly a fight breaks out in the crowd for some reason. Hopefully the players join the fray. Eventually the players do get to the voting booths, at which time I will ask each player to write their character's name and the party they are voting for on a little slip of paper and pass it to me. Players will gain their first level and superclass thusly.
Between that and level eight I'm a little fuzzy, but by the end of the session players should each have one of the sixteen main classes.
Eventually, at level 32, players transcend their class restrictions and become powerful wizards called Pathodynes capable of learning any skill or ability without penalty.

The challenges each player will face will depend largely on their class. For example, if somebody had the Inspector class, I would try to work some kind of murder mystery in there that they have to solve (perhaps occuring during that fight at the beginning?) Inspectors in this world are like magical CSI, using their sensory stats and equipment to find clues in order to find criminals which the other players, being part of the posse perhaps, help to capture. Or maybe one of the player characters was the murderer (which I will have discussed with the player beforehand.)
If theres a lot of combat characters in there though, like a Fieldmarshal, a Champion, and a Protector, I might have some kind of war break out. It all depends on what kinds of classes the players choose. I plan on tying all these events in the world together with some kind of prophecy about the arrival of a new Pathodyne bringing about a new age.

There will of course, be a lot of rival factions that players will be able to ally with and perhaps I can get some PvP action going (In one D&D campaign I had eight people and divided them into two parties racing against each other through a dungeon crawl). For one thing, though the world is primarily steampunk influenced, it does have it's own magical equivalent of the internet. Two actually. They are rivals (The concept of virtual monopolies is unheard of in this world. Competing subway systems twist and turn, crosshatch and spiral around each other.) One of these internets is called 'The Leynet'. Leylines occur naturally, but it used to be that they could only be used by people born with the gift of natural scrying (Druids). Eventually, to get more people to use the Leylines, the Druidic Order invented scrying aids to help the uninitiated, and are currently trying to get the funding to expand the network with artificial leylines. The other net is called 'The Stream', and works by carrying information through water. However, to get it to work, Arcanis Inc. (the owner of The Stream) has had to pour mass quantities spell components into the water supply. They insist that most of these substances, like fluoride, are actually good for people. When asked about the rising numbers of sewer monsters, their official response is "Correlation does not neccessarily equal causation." There are rumors that there is a shadow war going on between the Druidic Order and Arcanis Inc. A Pathodyne could put an end to it though.

I know theres some more things I have to flesh out, but thats about the idea that I'm starting out with. I hope theres enough there to work with.