1. You can enter zero as the selling price of the roof 2. you can allocate a percentage of the sale to the roof and the house, or 3. you can make a new asset entrty workseet with the roof cost added  to basis of the  rental and the roof depreciation added to accumulated depreciation and then delete the original work sheet. Since both assets are 1250 property, you may want to use option 2 or 3