Complex sentence: After the "No Man's Land" and "Cataclysm" storylines, Lex Luthor took on the task of rebuilding Gotham City, replacing many of Gotham's old art deco and Gothic structures with modern glass skyscrapers and buildings.
Split into simpler sentences: After the "No Man's Land" storyline, Lex Luthor took the challenge of rebuilding Gotham City after the events of "Cataclysm". Many of Gotham's old Art-deco and Gothic structures were replaced with modern glass skyscrapers and buildings.