Final answer:
The accountant should depreciate the remaining book value of the building over the revised remaining life of 10 years, following the adjustment in the building's estimated useful life.
Step-by-step explanation:
When the estimated life of a building is adjusted, the accountant should depreciate the remaining book value over the new estimated remaining life of the asset. This means that after 30 years of depreciation, with an original estimated life of 50 years, the remaining undepreciated value of the building should now be depreciated over the revised remaining life of 10 years. This change acknowledges the updated expectation of the asset's useful life and helps to ensure that the depreciation expense is recorded in a manner that more accurately reflects the economic usage of the building.