" This company who hired me buys the land and builds the building and then contributes it to the new LLC which was formed in 2020. " This sounds to me like the company (the first LLC?) that hired you needs to report it on their tax return. The later contribution of cash into the new (2nd?) LLC becomes part of their basis. 

It is possible I don't have the whole picture, but that is my take away with what I have read.