Either could be correct. If you made improvements to the property while it was a rental, you would list this as an asset - and depreciate it. When you sell the property, you would "allocate" (assign a portion) of the sale price to the roof.
For instance, if the property was $95,000 and the roof was $5,000, then 95% of the sale price would be allocated to the house, and 5% to the roof.
However, if you are just fixing it up after the renter moved out to make it easier to sell, you could add the cost of those improvements to the adjusted basis of the house when you sell it.
You know the facts and circumstances, so you get to decide which is the correct treatment - but you can't do both.
