[tedward515]

For a quick fix I would get some corrugated metal or plastic that you might see on a shed. I think it is rather cheap and can pick it up at most any lumber yard. You could attach it directly to the underside of the deck to keep rain, dirt and so on form falling on the car similar to what heel n toe described. Just be sure to angle it so that the water drains away from the house.

For a more permanent solution I would build a detached two car garage. It appears that you would have enough room for say a 24x24 garage, maybe larger. A 24x24 would give you space for two cars and plenty of tools. I don’t know if the fence represents your lot lines but I would put the front of the garage with a 20ft two car door to the ally and then have a single door on the back side so you have a pass through of sorts. If like many of us you end up with more than one p car you could pull it forward and park it under the rear deck and not take up all of your garage space. Just my 2 cents.