DOTA

That's a pretty vague question. It's no harder to develop than most other games--it just depends on what features you want to include in it, whether it's 2D or 3D, what methods you use to develop it (XNA is generally considered easier than DirectX10, for example), and of course, how strong your personal skills are.

Only you can really answer this question, in fact--you need to decide how you want the game to be designed and then assess whether you think you can successfully code all of the features you want in the game, scaling them back or modifying them as necessary, or learning new skills if you want them in the game badly enough.

In short, you're asking a question that we can't give you a good answer to.

i want it in 2d.. i want a simpler version..

what will i need to know to make it?

i want it in 2d.. i want a simpler version..

what will i need to know to make it?
btw,i use opengl..

1. A programming language
2. Graphics, Sound, and Input API
3. Data structures
4. Commitment

Just start making it, really. DOTA? What are you referring to, the whole Warcraft package or just the map DOTA?

Think about it, I don't think I could do the whole warcraft or even DOTA all by myself. There's so much to it. If you want a not so silly 2D game, why don't you try a shooter or a jump and run game. It's very attainable to some extent, and it presents the key concepts of game programming.