I've got two of these ancient buildings on my property, maybe a little more crumbled and collapsed than yours, and with larger building stones. I get signals, but can't lift the big stones out of the way to get to the find. The few successful digs produced rusty iron scrap and 10 inch spike/nails probably used for the extinct roof, so I have lost interest in my searching, but always have a gnawing feeling to organize the rock lifting with cables and a winch everytime I look at them..Maybe one day.
Good luck with your hunt.