There are no expenses to flipping a house, everything you pay out is part of the cost of the flip.
I set up a cash type bank account named for the house, street address usually. Everything I pay to flip the house is posted to that account as an expense (reason) for the payment.
When the house is ready to sell it becomes an asset, usually inventory if you are in the business of flipping. Create the inventory item, zero cost and qty, then "buy" the inventory item from a dummy vendor you create using the full amount in the house bank account. That will stock the item with cost and qty.
Later you sell the house inventory item. The cost will post to COGS, the income will post to income automatically.