Complex sentence: Manchester Courts, the tallest commercial building in Christchurch when it was built in 1905--06 and a Category I heritage building suffered serious structural damage and was the first major building that was demolished, with the demolition finishing just days before the 2011 Christchurch earthquake.
Split into simpler sentences: Manchester Courts, a commercial high-rise building built in 1905--06, was at the time the tallest commercial building in Christchurch. A Category I heritage building, it suffered serious structural damage and was the first major building that was demolished, with the demolition finishing just days before the 2011 Christchurch earthquake.