[Heel n Toe]

If you do end up with that house and decide to use the space under the deck, you will have to do something to keep rain and shoe grit and spilled beer and barbeque sauce and cigarette butts from last night's party from going between the boards and ending up on your car.

Or you could just hose it off everytime you pull it out. Heh heh.

You could build a few feet of shed roof (flat, shallow angle roof, probably covered with roll roofing) coming out toward the back yard to get more length to house your car and have room on the house end of the space for access to that basement door... and some shelves and possibly a workbench.

As far as how to enclose it, I would recommend the same siding that is on the house. Insofar as a door, why not a typical garage door, painted the same color as the house?