[Ian Robinson]

Looks OK , just the roof is flimsy.

I don't think you need council permission to put in a "garden shed" , nor do you need to tell anyone (announcing the construction of an observatory might also tell the local villians who will target it if they know it will house expensive stuff like a telescope or 2 or 3 , cameras, telephotos, a computer or 2 , etc.

I know villians will steal telescopes , as I had my Vixen FL104 + GP-DX knocked off (all conveniently - for them - packed up in metal cases , along with my set of LV eyepieces, my old Lumicon coma corrector and my set of 2" Lumicon filters) when someone broke into my garage and took them last year, a load of fishing rods and reels on the walls and under the rafters ($1000s of dollars worth) were not taken , nor my old Tasco and a couple of old GEMs , and my old 10" OTA which was standing in the corner with it's shower caps on, which were ignored.
The villian knew exactly what they were after I reckon and must have followed me home one evening after I'd been photographing the comet.
Took over 12 months - and I was treated like the criminal - to get a settlement from my home contents insurer. I got my settlement for my June Storms damage a lot quicker.
I've since quit that insurer and migrated over to NRMA.
All my expensive astro stuff has since migrated into the house taking over a bedroom , a locked garage is no obstacle to a burgler.