If you are a casual or occasional flipper, you don't list anything until you sell. At that time, you report the asset (the house), the adjusted cost basis (the price you paid plus whatever you paid for improvements), the selling price, and your taxable income is difference between the cost basis and selling price. If you bought the home in 2020 but did not sell it before 12/31/2020, you don't report the purchase or sale. You may be able to deduct certain of your carrying costs, as described below.
For the adjusted cost basis, you can include materials you purchased and labor you paid for but you don't get an adjustment for the value of your own time and labor.
You would not enter the expenses on a schedule C business unless you were in the regular business of buying, repairing, and flipping houses as an "ongoing trade or business"
For your carrying costs, you can deduct property taxes on any property you own, up to the $10,000 cap on state and local taxes. You can deduct mortgage interest on your main home and one second home, and your flip can be your second home for this deduction if you choose. You can't deduct utilities, insurance, or other carrying costs.
You may be able to capitalize your carrying costs, but this is unclear. Prior to the 2018 tax reform law, carrying expenses on investment property (such as utilities and insurance) could be deducted as a miscellaneous itemized deduction subject to the 2% rule. Or, you had the option to capitalize the expenses. That means you add the expenses to the adjusted cost basis. Capitalizing your carrying costs requires filing your tax return on paper and attaching a written statement. If you bought the house in 2020 and plan to flip it in 2021, you still must attach the capitalizing statement for 2020 costs to your 2020 return. See this answer for more,
https://ttlc.intuit.com/community/tax-credits-deductions/discussion/when-selling-an-inherited-proper...
However, the law says you can only choose to capitalize costs that are deductible, instead of deducting them. After tax reform, these costs aren't deductible, and the IRS has not issued a final ruling as to whether you can still capitalize such costs. If you want to capitalize your utilities and insurance, you may want professional advice. (You can also choose to capitalize your mortgage interest and property taxes, if you prefer not to deduct them on schedule A or if your itemized deduction is already limited by the SALT cap.)
