Your not likely going to get an idea of cost before you have more details. Costs change from area to area, so the cost would be a local thing.
You should not plan on building on top of the driveway, especially if it is to be tied to the house.
So you would start by developing a plan, size, shape, style and how it ties to the house and how the roof ties to the house roof and so on. The city may have something to say about it too.