Peter,

Still looking at wooden option as well, had a look at some examples. Main objections to wood is the permiability, its hard to control moisture and everything I've read suggests machine tools in a wooden workshop is the least desirable route to go. Also there's the maintenance. And its hard to make it as soundproof as a concrete or brick structure and thats important. Finally you can't site a wooden workshop within 2m of the boundary because its not non-combustible, so I'd have to make it smaller. Not that sure its much cheaper either! So while its still an option, its least preferable.

Another opton is timber frame but plastic coated metal box cladding over OSB as used on the roof. Again the soundproofing might be an issue unless I use a lot thicker foam.