The plans for the metal roof can easily be used for a double wide by ending the panels at the ridge and adding a ridge cap.
For approx 24sq of shingles installed by a contractor, you are probably looking at $6000 +/- $1000, for decent shingles. This would include tear off and hauling away old shingles. Probably about $1500 worth of materials for a DIY.
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All information and advice given is for entertainment and informational purposes only. The person doing the work is solely responsible to insure that their work complies with their local building code and OSHA safety regulations.