If I paid for gutters(replace)/ soffits (installed) on my rental home in 2018, but the work was not done until 2019, in which year do I report the expense/improvement?

If you paid for the gutters/soffit and installation in 2018, then you will include that cost on your 2018 tax return.

Please see TurboTax TaxPro Coleen's response to a similar question: https://ttlc.intuit.com/replies/6149380

If it's more than $2,500, then...

Replacements of all the gutters and soffit of your residential rental property:

• Are generally restorations to your building property because they're replacements of major components or substantial structural parts of the building structure. As a result, these replacements are capital improvements to the residential rental property.
• Are in the same class of property as the residential rental property to which they're attached.
• Are generally depreciated over a recovery period of 27.5 years using the straight line method of depreciation and a mid-month convention as residential rental property.