That's the reason I even am thinking of a 12ft door - a little more room for equipment.

If I do use a 12ft door, I'm going to see if they will put in a header and jam for a 16ft door too. So if I did want to convert from 12 to 16, it would be an easier operation.

The slope to my alley is probably going to be the deciding factor. The alley slopes too, so one side of the drive is going to be steeper than the other.