Parking under shade i.e a porch, your minimum wall to wall width as mentioned above should be 16 for comfortable parking. Else you can make a 10 feet wide porch for one car if wider porch consumes covered area spoiling your house spaces, and for the second car you can leave extra open space from the front wall and use compulsory lawn area. I will try to post a reference pic for a smaller 5 Marla 25x45 house i planned for 2 cars.
Architecture is the art of how to waste space