Couldn't you just make a TC (total conversion) mod for oblivion?  IIRC I know its possible in Skyrim,, don't know/recall anything about oblivion.  Scratch that... just did a quick search and there are TC mods for oblivion.

4 hours ago, Dusty Cane said:

i am not looking to create a mod but a game of my own

That's why I said a Total conversion mod... the only reason against this would be if you wanted to sell your game.  But a TC mod can use your own assets, game rules, story... and so on.  You can also use stuff from the base game either for real or placeholder art.

4 hours ago, Dusty Cane said:

(mainly because my pc is pretty bad)

One, what are your PC specs?  CPU, RAM, Video card.  Also just so you know developer machines tend to be more powerful than the machines used to run the game.

Oblivion used an engine called Gamebryo... its not free and might not even be for sale anymore.

The only free engine that off the top of my head supports asset streaming is Unreal.  Asset streaming is what allows you to have very large worlds with a limited amount of RAM.

BTW a lot goes into making an openworld game I really wouldn't try it as a first project.

Again what are your system specs, so people have an idea of what the development tools needs to run on?  And judging by your response you don't want a engine you have to pay for, right?  Basically I'm saying you should give more information so people have a better shot at helping you.

You could always make your own engine.

edit - Lumberyard also might some form of asset streaming although I don't know at what granularity. Here:

First of I would just like to point out that the response time on the forum could sometimes take a while, having to wait a day for a reply should not really be considered "long", people are usually very good at giving advice here so just have patience

With that said, I know this has been discussed many many times before but a good first thing to consider is which amount of time and resources your are planning for this project. I am not saying that it cannot be done but keep in mind that the amount of time to make even a "simple" open world game might very well be a couple of years of hard work. Are you planning of doing all the coding, level design, asset design (graphics) etc by yourself from scratch? Or will you be using paid models or pay an artist to make the game?

I am not trying to demotivate you but when people are getting into game design it is quite common that they seriously underestimate the time and resources that goes into making a game. A game-engine is by no means a magic bullet that makes you finished a massive open-world game on your own in a couple of months, not even for a seasoned developer.

The most common advice you will get here if you are new, and it is a good one, is to start out making a few simple games in order to get a base understand of what is required in order to design a game. You might already have done this, and in that case its fine but in most cases this is not quite true.

So, what are your current "budget" for making this game? How much time are you willing to put in? Will you have money allocated to buy resources or will you be making them yourself? Are you willing to hire external help (i.e pay them) to make resources etc for your game?

These might sound like "boring" questions, but the kind of engine people will recommend will depend a lot on the scope of the project, especially for what sounds like a quite big project.