Well thank you very much for your thoughts, peeps - unfortunately Wiley's SWMBO encapsulated the result. I went and took a long hard look at the workshop with a tape measure, and if it was a hollow shell it'd be big enough. But it's not a hollow shell and thus for all practical purposes a no-go. Also a more practical assessment of the access and such wasn't encouraging. The garage would have been okay - but the Old Man has this quaint idea you should be able to get your car into the garage. Yeah, I know, I don't get it either but what can you do? So an opportunity missed.
Heigh ho, not all a loss 'cos in the course of researching about such things I ran across this blog which is entertaining and I shall keep up with it regardless. I'm not by nature a glass-half-full kinda gal, but I'm working on it... ;)