Disregarding the diminutive scale of the inhabitants of this room, it is a very sinple build: stone and lime mortar foundations to a meter or so down. Walls of rammed earth, cob, cordwood, adobe, strawbale or rubble stone, timber frame etc. (anything works as long as it is solid). The walls and ceilings are plastered (clay or lime or whitewashed mud), wooden floor boards (anything works but oak is best). The fireplace stone surround should be granite but limestone works for wood fires in a pinch, backing should be fire bricks if possible (pricey but lasts virtually forever) ceiling and upper floor joists are timber framed. Window is a wood frame with lead cames (DIY eminently possible). Outside? I'd do plastered walls and a thatch roof (straw or heather but reed is ok in a pinch, because mice right?).
https://hell.twtr.plus/media/4f0e2de622363d2cb954982e6008e6e4fc0e2453228c6688515eb558511769ad.file
