We built our new 1450 sq. ft. rancher with attached 1250 sq. ft. 4-car garage in 2003. I paid for 30-year IKO asphalt shingles, but only got 15 years out of them. When I replaced the roof, the contractor stripped the old shingles off, disposed of them, and covered the sheeting with GAF membrane. He replaced all the roof vents, even adding a couple more. Where the original house builder merely overlapped the shingles in the valleys, this contractor installed new metal valleys and flashings. The new GAF shingles are fibreglass substrate, instead of normal asphalt paper. This contractor is one of the best in my area, and even redid the roof on my 10' X 14' garden shed. After the crew was done, they cleaned up any loose nails, debris so well, there was no evidence of them being there, other than the new roof covering. Their price was $11,000, taxes included.
A couple of years later, my neighbour replaced his asphalt shingles with steel roofing. From the road, it looks like normal shingle roofing, not like something used on a barn. He has an 1800 sq. ft. house with attached 3-car garage. His cost was $30,000, but should last a lot longer. He is 20 years younger than me, so will get more use from his new roof than me.