Steve is correct here. First, discuss the matter with your agent. Have they been in contact with the builder? What is the cause for delay in construction?
Second: Read your contract to the builder, to determine if there is a "non-performance" clause which should clarify what to do if this occurs.
Third: There is a binding contract in place. Therefore, seek the advice of a licensed real estate attorney who will be able to tell you what legal remedies you have available to you.
Fourth: To address whether your agent should have brought you to the site,,,if the property fit your needs (and it apparently did) then yes. As agents, one aspect of our responsibilities is to introduce buyers to properties which fit their specific requirements. A professional realtor will introduce you to all the properties availabl. However, having said that, it is the realtor's responsibility to ensure that they have all the pertinent information on the property. I.E., in this case, did the realtor do research on the developer? What was the outcome of the research? Anything to indicate that they "promise the moon" but deliver only a paper sample?? If the agent did their job then yes would be the answer to that part of your question.
Always, always, always, READ THE FINE PRINT of everything you sign!
Hope it all works out for you.
Tina Evans, Principal Broker