To honestly answer your question as to Plainfield real estate I must ask what specifically are you asking?
I can tell you that in the past 6 months there have been 325 closings in Plainfield ranging from $80K to over $600K. This speaks for a very active market to which Plainfield has been over the last decade or so.
As to your builder question I am not familar with John McNaughton or any homes being built in Plainfield by him but as with any builder I sugest you contact the better business bureau and do your homework. I also strongly suggest you use a realtor to help assist with your negotiation with the builder, remembering that the builder is going to do what is in their best interest while a realtor will be looking out for your interest. Also they might be able to provide some additional inisight and suggestions that might not otherwise present themselves.