Scenario: Land with established home purchased in 2010 for $500k. Loan of $400k. Lived in as PPOR until 2015. Demolished in 2015 and a duplex constructed on land. Cost to build is $800k including plans, permits, subdivision, and construction. Both townhouses in the duplex are identical and occupy the same amount of land. One townhouse is retained as PPOR, one is sold. GST applies to the sale as it is a new dwelling, using the margin scheme. Question: what can be added to the cost base? Some or all of these? 50% of: 1. original purchase price 2. pre construction interest 3. during-construction and post-construction interest 4. original conveyancing fees 5. Original stamp duty 6. scrap value of demolished house 7. construction costs 8. planning and design costs 9. Real estate agents fees Anything else?