I have a two-car detached garage with an asphalt floor and a wooden sill plate. The sill plate rests on the ground, and most of the year, the ground is wet. The sill plate has rotted along most of the ground, with the support 4x6's directly on the water-logged ground. As a result, the garage is leaning towards the back, tilting the garage door and leaving a gap where it meets the floor. Also, as the snow is melting, water is creeping through the rotten plate and onto the surface of the garage floor. What can I do to fix the problem? Jack up the garage and put in a new wooden sill plate with pressure treated wood? Should I (could I) try to put in a cinder block concrete base with a new sill plate on top? Can I do this myself? Thanks!