Complex sentence: Initially the façade of the stadium would be covered with crystal, but Dünn Lightweight Architecture made a new proposal with ETFE because of the many advantages that ETFE had over crystal and any other material for that particular project.
Split into simpler sentences: Initially the façade of the stadium would be covered with crystal. Later on Dünn Lightweight Architecture made a new proposal with ETFE because of the many advantages that ETFE had over crystal and any other material for that particular project.