I thought I could solve the vagrant problem by buying and repairing the buildings.

Class D Property:This is where we find many older properties of more than 30 to 40 years old, in need of major repairs.

Quote from @Dan Grove: Some combination of cash to seller, closing costs, repairs, construction, paying off arrears, assignment fees, commissions.   

Nothing to get crazy about but no need to deal with tenants, property taxes, repairs, vacancies, etc. just sit back and collect.

Use tax benefits like depreciation, repair deductions, and tax-free refinance proceeds to offset income, and consider an LLC for liability protection.

That aside, If it were me I'd get a professional estimate of what repairs would cost, and make the decision to keep or sell based on that. 

And you need to keep detailed records of all repairs and improvements.

Mortgage rates at 7% 2. 25% down3. 10% of current rents budgeted for capex, monthly repairs and maintenance and property management fees. 

Aside from downpayment, you want to have a solid emergency fund in place, something that can cover unexpected repairs, vacancies, or any other random costs that pop up.I’d also recommend saving more than you think you'll need and keeping a close eye on your expenses.

Adding the rehab money is standard if the property needs repairs.