Good cus the kit would get wet otherwise

That’s a good idea. Obviously the size of garden will potentially dictate how big and what material you will use to build it. Not forgetting potential planning permission issues.
Before I found our house with the benefit of an extra room, I did think of a solid log cabin with sound and insulation proofing. It was about 6x5m internally and would have cost 23k done probably. Sounds a lot but going from a three bed to four bed house costs the same.
If you don’t need loads of bedrooms and can find a nice house with a good size garden, it’s a great idea. I was very close to it.