As the city struggles to make a dent in Baltimore’s 16,000 vacant buildings, officials say the DIY plan shows the lengths they’re willing to go to if it means they can fix up a whole block at a time. But the experience so far underscores how hard it is to turn around even a single block in a struggling neighborhood. Challenges include crime — a woman was found shot dead on the block in June — the borrowing ability of potential buyers, and a mix of occupied houses and vacant buildings in various states of ownership.