I have the same configuration of garage you have. I just got a roadster 4 weeks ago and it sits in the garage when not in use. This coming week I'm getting a 240 socket put on the side of my house along the drive way, where I'll be parking my model S when I get it, and where I will charge the roadster when I want/need fast charging, which hasn't been an issue yet.
The socket will go on the side of the house and will have a small bird box like overhang to protect it from the elements. The side of the house it's on already has a 2 foot overhang on the roof and stays dry when it rains, which is quite a bit up here. I have the mobile connector cord which is rated for outside use. I will have it hanging on the wall when not in use or stored in the car or in a rubbermade tube along the drive way.
As you can see, it really shouldn't be an issue for you. Also, I have yet to put more than 80 miles a day on the car, it recharges just fine on 110 to be ready for the next day, which has been a surprise to me. I expected to need a 240 or 70 Amp charging station before I took possession of the car, in the month I've had it, it has not been an issue. I still am putting the 240 in to have it when I need it, which if I have it, I'm sure I'll utilize it by taking longer trips on consecutive days, especially as the weather gets nicer up here. Also, they are not 100 percent sure what the standard will be for the "socket" for charging the Model S versus the roadster. I bet the Model S will have the same connector as the Volt and the Leaf, which is different than the roadster. Having a 240 connection and not a dedicated telsa charger/Clipper Creek charger kept my options open for having two EV's which might have different connectors. (I'm sure Tesla will have an adapter for the Roadster by the time the Model S arrives, but it seemed a reasonable solution to me.) Also it was easy to add a 240 outlet to my existing panel, it was not going to be so easy to add a 70 Amp to it for the high speed charger.
Hope that helps.