1) The cost full cost of the Leasehold Improvement is added to the full cost of the Building.
2) The amount you were able to depreciate for the Leasehold Improvement is added to the amount you were able to depreciate for the building.
3) Your "Adjusted Basis" in the building is usually #1 (above) minus #2 (above).
Does that answer your question? If not, please post back with further details.
