Having ordered the Smithy Set it occurred to me that I would have to construct a smithy (Aargh!). Wills Kits produce an impressive range of hard plastic textured sheets: brickwork, stonework, cobbles, paving, planking etc for the model railway market. They also produce a number of kits including the barn above and a (too) small smithy. Further "antiquing" could be achieved by substituting, planking or pantiles etc. - from their range - for the slate roof (sadly, no thatch). The kit was simple to construct and paint and reasonably cheap (£4.75). I wondered about giving the barn a bit of "medieval sag" with a hair dryer but lost my nerve....
Wills don't seem to have a website but a good few model railway online shops seem to carry their stuff. In the UK, Ian Allan and Modelzone stock Wills.

Lovely barn!!!
Wills kits became Finecast
http://www.sefinecast.co.uk/Contents.htm
and the houses etc were bought by PECO
http://www.peco-uk.com/