I've already done a description of a modern building here, but the examiner might ask you to describe an old building. How can we adapt the 'modern building' description?
Looking at the vocabulary I used to describe the modern building (famous landmark, spectacular views, best vantage point etc.), it seems that we should choose an old building which is tall or has great views of a city.
One possibility that comes to mind is the Empire State Building in New York. It was built in 1931, so I think that would be old enough.
Can you think of any other examples? If you choose a famous building, it will probably have its own Wikipedia page. Do some research, and plan your description.