Complex sentence: The boom in Mexican construction industry at the beginning of the 21st century has reached Condesa, which is being packed with contempo-minimal-styled apartment buildings and trendy lofts, built where old single-family houses used to be.
Split into simpler sentences: The boom in Mexican construction industry at the beginning of the 21st century reached Condesa, which was being packed with minimalist apartment buildings and trendy lofts of contemporary style. These were built where old single-family houses used to be.