I've taken a different approach to reporting flips based on a conversation with a tax partner at KPMG.

On the Sch C in the revenue section I create a supporting worksheet showing the gross contract price of each house sold. In the cost of sales I create a supporting worksheet of total cost basis (purchase price + capitalized settlement costs on purchase and sale + improvements) of each home sold. Then of course any G&A expenses in the body of the Sch C.

But to avoid any matching issues with the 1099-S I also report on Sch D the 1099-S (contract price) of the house and a cost basis exactly equal to that to reflect a -0- capital gain. The description on the Sch D is the home address with a notation this is reported on Sch C.  The only reason again is to avoid any potential matching issues.