i install metal roofing and i can tell you that if you buy a good quality metal roof, it doesn't only last a long time, it increases the value of your home. shingles need to be changed every 15 or 20 years at most and plastic can get damaged by heat and extreme cold.
No any concerns about buying a house with a metal roof, but in Cincinnati most metal roofs is commercial. My Opinion as a roofer and home owner is to have shingle roofing because its easy to do any roofing repair on it.
Not a roofer, although I've done some, and I agree. I wouldn't want a metal roof - I've had to repair some in industrial buildings and it isn't real easy. They are also noisy though that would be alleviated with an attic and ceiling under them.
I have replaced my old asphalt shingles with a metal roof and you must get someone experienced. Some will try to save money on not waterproofing around the roof vent pipes. Get a few estimates and references.