If you don't want to Jack the whole building, you can convert your trusses into a stacked roof, Depends on how your trusses are built, anyway you place Jacks on the truss roof supports, rip out the bottom of the trusses, Tilt up a ridge beam size depends on how big a span your working with and live loads etc. then you cut the front of the garage to height put in your door header, add a support piece for the new ridge beam. You will have to build a similar support on the back end of the garage. The trick is placing your jacks so the roof doesn't fall in on you head when you chain saw out the truss innards
You may have to install 2x6's also because the 2x4' will sag like mad.
You could use steel or wood for the new roof support. I don't think it would be cheap, good luck finding a carpenter whose not afraid to redo
your roof from the inside but it could be done.
Maybe somebody experienced in major termite repairs will know how to do it for you, I suggest getting a steel building why collapse your house