Flipping and cogs and inventory

[Leanne NA]

Bought a house in 8/2016,  didn't sell until 2/2020. Never included it on any taxes. And trying to do 2020 now. Do I skip inventory and just enter the cogs as purchase price plus Reno over those years? Also, if using inventory, am I supposed to expense the Reno cost, or just inventory using purchase price? And only add in Reno when I sell in the cogs total?. Thanks so so much