OK - so I went for the outbuilding construction solution. Let's have a "shed" at the end of the back garden.
Then I discovered that, just because I live in a National Park, it could not be just any old shed. It had to "be in keeping with the area, and matching/complimenting the other buildings, and regulations restricted to only a small 20m^2. That's roughly 18' x 13.5'.
So it ended up with pitched roof and matching tiles and render. With it comes infrastructure of 10mm^2 of 240Volt SWA power feed line in 110mm duct, with a 25mm HDPE pipe water supply, and sundry network and other cables. Insulation, radon gas barrier, patio-type paving, it just went on and on. I think it counts as a fairly bad case of HM-style "project mission creep"!
I did kinda go a bit OTT on the provision of power sockets!
The suggestion by
@tjb seems relatively simple and practical in comparison
Sadly, even now, there is still not much room left around stuff back in the garage
BUT - even though small, the lathe, mill, drill press, bench, easy chair and small refrigerator can all fit, and it has now become a winter insulated man cave with a great view!
...
Then again, the outhouse now needs it's own further "outhouse", to put the compressor, store gas bottles, engine hoist, and other clunky stuff.
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