After much dithering and drawing and research and belt tightening, an observatory is born. I'll update as things progress, here are the first two weeks activities with a before shot to start with.
A basic overview: A split level observatory (due to the slope of the block) 6x3 meters (If you haven't read/heard the story, the short version is my lovely partner said "Are you sure 3x3 metres is going to be big enough

, so it's 6x3). Basically 2 Titan garden sheds joined back to back. The long dimensions run SE (lower end) to the NE. Positioned as close to the front boundary as councilly possible

, which puts it at the highest point of a very sloping block. A good 150 metres to the creek at the bottom.
Rather than excavate great whopping cut and fills everything will be on stumps. The whole construction apart from the floor itself will be steel and villaboard/hardiflex. I believe in overkill. Plus if I ever need a doghouse I will be safe and comfortable in a cyclone.

Plus stumps will get me higher off the ground.
I've included some of the plans I've been drawing so you can try to get an idea of how it will look when it's finished and how it will sit on the site. As mentioned before the first shot is a before shot taken a few weeks ago, then a shot from last Friday after finishing the profiles and then from yesterday after a few hours of pick, shovel and crowbar. There are 15 postholes all up plus a good bit of excavation. I feel fitter already.
Anyway, now that it is underway I'll post weekly updates hopefully (well at least fortnightly) as construction proceeds. I hope you get some ideas for your own observatory out of this adventure.