A house with no comps?? Need Help Again!!

[Karen Hurd]

Hello everyone,

I hope you are having a wonderful day. I have a house that I want to put in a cash offer on but I can't because there aren't any comps. It's a prime location, excellent schools, but the guy who bought the house in 2007 is a builder.  He turned the house into this massive house that doesn't exist in this town/neighborhood. Most of these homes are 3 or 4 bedrooms and 2 and 3 baths. This house is 6 Bedrooms, 5 baths with all kinds of legal extensions. He's a younger guy with young children and his wife died of cancer and he went completely broke. He is going to put the house up for sale soon and my brother feels he will take cash for it. 

What do I do in this situation?

Thanks in advance,

Karen