I just started creating an idea with Unity3D engine and it's RPG (mostly), but i don't know how to make one and how the upgrade tree works and how should i make it fun and other things in RPG games.
i searched and there wasn't any good article or book on making an RPG game , or maybe i didn't search well.
So, i was searching for a good article or book on this topic.
Thanks
there wasn't any good article or book on making an RPG game , or maybe i didn't search well.
Or at all, maybe? 
Bing yields 155 million hits for "programming a role playing game," and 7 hits specifically for "programming a role playing game unity." If none of those suits you, you're probably out of luck.
there wasn't any good article or book on making an RPG game , or maybe i didn't search well.
Or at all, maybe?
i mean in general not the programming part. just tells how it works and the programming doesnt matter
Could you be more specific on what you mean as far as 'how it works'? There may be some write-ups or something someplace, but finding anything as substantial as I think you are looking for will be extremely challenging. Part of the reason for this is the material doesn't really exist.
Going off just an in general sense:
If you are just curious about generic elements, say NPC dialog, the best resource for these are the games themselves. Just be sure to look at it from a purely technical point of view. In other words the story doesn't matter. What matters are the underlying systems for these things. From there it's relatively easy to extract the basic idea and think about how these would have been done. Skill/Tech trees are also shared across a wide variety of games, which are really just abilities or structures that have pre-existing requirements to unlock. Thinking of it in terms of pseudo-code might help you as well.
Hope that helps! 
https://www.rpglibrary.org/articles/storytelling/36plots.php
http://en.wikipedia.org/wiki/Attribute_(role-playing_games)
Here are a few resources you can check out.
There are tons of ways to make a RPG.
RPG means Role Playing Game, so it is a really broad category.
You need to be more specific..
Let me link you to a Github project where there is code for the d20 rpg combat system: https://github.com/mcferno/d20-rpg
There are several licensed "rpg systems".. Dungeons and Dragons (dnd / d20) and Das Swarze Auge (Dark Eye/DSA), so you need to shell out for an industrial strength rpg engine.
But there are lots of people who have created a RPG, with various levels of success/completeness.
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Some more resources:
To be honest, an RPG could be boiled down to a set of rules and a 20-sided dice.
Like this: https://github.com/TeamQuadForce/Comp345RPG
Wizards of the Coast - where my avatar is from (red wizard) - sell their dnd system: http://dnd.wizards.com/
They have a nice overview of the rules.
If you read German, search for Das Swarze Auge (The Dark Eye) - they have an extensive wiki about the system.
One place to start is making a list of RPGs that you liked, and then listing what you liked about each one. This is the raw material you need to make a features list or a story concept, depending on whether you want to design the gameplay first or the story first. Or you can work together with someone who already has an idea for an RPG they want to make.
Wouldn’t it be a good critical-thinking exercise to figure out on your own how to “make” an RPG? I’m assuming the main problem is how to keep track of quests and progress sequentially through the story.
And there are a billion ways to do that. Some better than others but you don’t need the absolute best method.
Why not grow yourself and get into the good habit of doing mental exercises such as these? It only makes you stronger.
L. Spiro
it's RPG (mostly), but i don't know how to make one and how the upgrade tree works and how should i make it fun and other things in RPG games.
i've been a player for 38 years, and a ref and DM for 37 years. statements like this make me want to cry.
lemme see if i can keep this brief... i've been thinking of posting a blog entry on the topic....
a rpg lets the human player play some role other than themselves. the setting as to location and time period can be anything. real world, or fantasy or imaginary, or the far future or distant past. as creator of the rpg, its your job to define the rules of the "universe" you're going to simulate for the player to role play in. thus the reference to paper and pencil rules and a d20. levels, power ups, storyline, queist, and all those other stereotypes associated with rpg's are different designers takes on the "rules" for their universes. IE its how they model and simulate their game world. or at least it supposed to be. nowadays, folks don't undertsnd this, and think RPG rules are a well defined set f game mechanics, the way RTS's have "build building and units and destroy the other guys building and units", and side scrollers have "jump and shoot". unlike RTSs, side scrollers, tetris, etc, RPGs are not a set of game mechanics that it has been discovered makes for good entertainment. they are various attempts to model a game world. think in terms of how rpgs you are familiar with model this or that in the game. how do they model combat? experience? skills? and so on. don't think you can just pick game mechanics x,y,z,and w, and boom, i've got a fun RPG.
