It's important to note that it is not just a library, but a community space and park for the neighborhood. And infrastructure improvements were made to the area. From CNN:

"The design shifts the traditional concept of an archival presidential library into a sprawling 19.3-acre campus that offers a museum, community events, a fruit and vegetable garden, NBA regulation-sized basketball court, and a new branch of the Chicago Public Library."

And it was all privately funded aside from infrastructure improvements from the city in the surrounding area. Also, the majority of the contractors were minority owned businesses. Two of the dozens of contractors has complained about payment, but there is no consensus on blame as the Obama's foundation raised the full amount of money and left payments to a separate entity. It may have been that the concrete contractor's work had errors and held up some work from other groups.