Mills Building development in El Paso, Texas. This 12-story, 138,000 sq. ft. structure dates to 1911, when it was among the tallest monolithic concrete buildings in the United States.Vacant for years, it is part of the larger $67 million Mills Plaza redevelopment. This 12-story, 138,000 sq. ft. structure dates to 1911, when it was among the tallest monolithic concrete buildings in the United States.Vacant for years, it is part of the larger $67 million Mills Plaza redevelopment being undertaken by Mr. Paul Foster. This catalytic investment is taking place in a census tract with a poverty rate in excess of 50% and an unemployment rate exceeding 20%.