I just did a cedar house yesterday. It wasn't shingles, just lapped siding. If it's painted, your usual house wash should work for mold, mildew,dirt, etc. If anything, you may need to increase your bleach slightly if the mold/mildew adheres due to the texture of the wood.
If the paint is not really intact, the whole house probably needs a restoration and repaint/stain. That isn't my expertise, so I can't help you on that.
