Accounting treatment

The existing building included dismantling costs as part of provisions and you already received tax exemption to the extent of tax rate.

Reverse the provision when dismantling starts

The building is usually measured at cost in the subsequent years. If it is revaluation method, the surplus is transferred to equity. 

Depreciation ceases the moment you classify the asset as held for disposal.

The carrying amount of existing building will be derecognised.

The loss on disposal is recognised in income statement, (disposal proceeds if any- carrying amount)

This is IndAS 16 treatment. Let me know if your followin* AS.

When your constructing a new building for personal use, account for expenses.

Once building is completed, recognise asset and meantime, 

Include the construction costs into the cost of asset.