I have shingles on my house and I had a construction crew put a metal roof on. They put the metal roof on over the shingles with nothing inbetween, i have heard you should either put some form of material or wood strips inbetween the two. Which is the best way? Also they didn't put any vents on and last winter (our first with the metal roof) we had quite abit of moisture in the attached garage. Do we need to put in vents? If so which ones?