Question

how have historical buildings and painting prove useful as a source of history

Answer 1

The following points may help you:

a Historical buildings and paintings are important sources of history as they give  important and detailed information pertaining to a particular period.
b. Inscriptions or the written records engraved on stones, pillars,clay or copper tablets, caves and walls of the buildings provide detailed information. 
c. They help to explain chronology of events, important developments substantiated by material evidences monuments, art and architecture.
d. It provides us with a more unbiased information.
e. Paintings depict life and culture of a particular period.