Company Viral Game for Christmas

I am looking to have a game built for the purposes of marketing and would ideally like something fun that would increase the chances of it going viral. I have never had one of these develeoped before and have no idea what I would need someone to do, but I would be interested in getting prices, what you can do, ideas etc etc. Our business is in the property market and we would ideally like a game based around the home/houses. Please let me know your thoughts, ideas and prices and timescales. This would ideally be a link back to our site. Thank you for your time!