What's cost basis of a house built overseas from scratch?

Hello,

I'm new to this forum. I understand taxes, but this issue is not 100% clear to me. About 20 years ago I received a land (gift) from my parents overseas. Over the past 20 years I've been slowly building a one family house. It takes a while because I live in the US, also, my father helped me a lot. My question is, what's my cost basis? Is it the land cost which i received as a gift and then added construction cost or everything combined. I have majority of receipts, but I'm sure some are missing. Also, is the IRS going to approve handwritten receipts from contractors showing their work and charges. Some contractors in Europe were not required to provide receipts and we don't have capital gains tax per say. In my country after 5 years of owning property you're free to sell it even with profit and you don't pay any income taxes. Thanks a lot.