I routinely price my frames by the sq. ft. and don't see why it's a hard thing to do. You can only cram so many timbers in a given space. I would have no problem quoting his 24x32 saltbox using planed white pine at about $17,000.00 assuming there is a loft.
I'm not trying to get the job since my schedule is already full for the year, just trying to make the point.

www.mktimberworks.com