It is very important before you buy a used home, to get an estimation of its renovation costs from an engineer or a professional contractor who is expertise in renovations.
The cost of repairs depends on the works you want to do.
However, the large volume of repairs-renovations ranges from 100-300 € / m2, except for very light renovations (e.g. only paintings). The essence, however, is that a decent internal or external renovation gives more value to the property and makes it more "easy to sell" or very easy to lease, with the result that the owner is the winner.
Especially in investment properties, the time that a property is empty reduces its value of efficiency, therefore its profitability.