C,
the guys have hit on the usual, spacers followed by drywall inserted in the gap btwn the post outer face and the wall material inner face. In your climate, with all the materials on site you could drywall to the posts directly and follow by the siding as has been suggested. If you can get longer drywall (12' or 20') put it up horizontally so the seams go across.
You still have the problem of how to run your electric. Have you considered any of the plastic raceways for hiding and neatness ?
The roof material I would use would be metal, not tile. This also gets you some airflow brwn the roof and the shed interior.
Good luck,
Deralte
