My electrical panel is in the basement on the west end of the house and my garage is on the east end. I had planned to run a 6/3NM-B cable along the joists and through the rim joist to get into my garage to feed a 60 amp subpanel. That has proven to be a much bigger challenge than I expected, so now I'm thinking about running THHN from the main panel to the outside of the house and run it through PVC conduit along the north wall and then run it back into the garage wall to feed the subpanel. I would use #6 (red, black, and white) and a #10 green for ground. Does this sound like a reasonable approach? It feels a bit hacky to go outside and then back in, but it's going to be much easier than the other approach.
I learned here on the stackexchange that running wire outside is considered a wet location and THWN wire is needed, even if its in conduit.. The W is for wet locations.