"I want to have many cars."
Translation:Eu vreau să am multe mașini.
Avere has a few related yet slightly different meanings based on the context. Sometimes its plural averi is used instead.
El are o avere mare. or El are multe averi. can both mean that he is rich or that he has many belongings. But it doesn't really state how rich. It is often assumed that the person you are saying this to is aware of their wealth, and you are merely pointing it out.
Averea mea. means my belongings (which is why it has its root in the a avea verb). You don't even have to be rich to say this. Even if you are poor or own a few things, you could still refer to your belongings like this, though it would be a bit strange to do it proudly.
Vreau avere. means that I want wealth, but it's not saying anything about whether I want lots of money, or expensive cars, or lots of houses.
Ea are avere de la parinți. would mean that she has her belongings, money or simply riches inherited from or given to by her parents.
El a făcut avere/averi crescând oi. would mean he became wealthy by raising sheep.
As for I want (to have) many cars. you can say (Eu) vreau (să am) multe mașini. but we would rarely say să am in this scenario since it's obvious what we mean. We cannot say Vreau avere mașini. or anything like that.