First of all, a good initiative.
Now, you will have to start your homework right now- Ask the general population what they want in a car from Econo-boxes to middle class cars and luxury ones.
Summarize the points then start looking at the cost of producing them.
Will you use your own engines/ body parts, what will be manufactured here and what will be imported.
How sales and after sales service will work, then you can present all this info to interested investors and banks.
Ofc, you will have to compete with the big three fraudiyas here and beat them!
It requires a lot of money and is a hard thing to do. Once you're on your feet, then it will go smooth as butter.
First year, you might face a bit of loss, then Inshallah it will go at a fast pace- Once your name is on everyones tongue, then you're sorted and can hire me as a Manager 
Sorry for limited knowledge, not in this field 