This assumes that each home has not already been stripped of copper, which is not the case. Most of these homes are bricks and wood.
EDIT: Some links. Copper theft is a big deal in Detroit.
City of Detroit borrowing a page from scrappers and thieves by selling old copper wire to boost Detroit's finances.
http://www.detroitnews.com/story/news/local/wayne-county/201...
Thieves stole copper from functioning pumping stations, leading to massive flooding in Detroit recently
http://detroit.cbslocal.com/2014/08/13/copper-theft-a-possib...
Copper thieves caught in a sting on camera
http://www.wxyz.com/news/local-news/investigations/copper-th...
The purchase of homes in Detroit is NOT to sell or repurpose ANYTHING.
I work downtown, and drive through these neighborhoods every single day to avoid traffic (thanks Google!).