Complex sentence: Later, another story to make it four stories, and then a two story annex with views down to Pok Fu Lam was built, and then a further addition doubled the size of the annex and added a third story.
Split into simpler sentences: Later, another story was added to make it four stories, and then a two story annex with views down to Pok Fu Lam was built. A further addition doubled the size of the annex and added a third story.