Thanks guys for your comments.
Yes Joe that's where I build/spray/ with shelves/lights/heating. After 40 years of marriage my wife wanted the dining room table back, something to do with family coming over for Christmas Day dinner!
We don't have basements here in the UK. Well you do if you have £1m+
To build on the back of the garage as we are on a sloping site/split level I put out four tenders and all came back around £40,000!
So we went to a factory about 30 miles away who make various designs of garden buildings/conservatories etc. So I chose one about the same size of room I wanted, in double width logs, in the sale it was, with electrics,insulation, all nuts, bolts, screws, hinges, flooring, roof shingles and double glazing (standard on all buildings) £2,400! Slightly less than a brick built room. It took me and my wife one evening to put it together, one day to paint it with the oil based stain supplied and one day to fit and hang the doors and windows. Two hours for an electrician friend to hook up the electrics to the house in armoured cable (so I don't electricute myself digging the garden) and hey presto ready to go.