What should I do about a porch and porch rails?
If you hire a "roofer" to re-shingle or install a metal roof, they generally are specialists and don't do carpentry. You'll want a carpenter or general contractor to build the porch roof and railing. They would certainly complete the porch roof, and depending on what's involved, may be willing to do the house roof too.
Local codes come into play with anything that is actually attached to the house. In my town the first thing they would look at would be the foundation and footing of that slab. My deck for instance, is on concrete tubes that only go down 3 1/2' Not the four they want, so I am not allowed to put a roof on it unless I have those redone.