Paul - I just built a ROR obs - I did stop counting costs half way
, but it turned in around $3k I think, and took about 2 months - mainly weekends and a 6 day stretch of time off work. That was including a chunky concrete isolated pier, and used ply-clad stud walls, gable roof with colorbond roofing and also an alarm. For power I have used an extension lead I plug into a caravan/boat inlet on the wall, but will likely have her hardwired once we get some other work done in the yard.
I have kept a web page with construction details -
link.
Link to my DIY thread here too.
Cloudynights also have a pretty active observatory forum - good info. A good link for heaps of amateur observatories is
here too.
One thing I
would change for Mk-II is to have the roof roll
towards the computer/desk/etc end, that way you can partially roll off and dew-shield yourself!
If I had more space I would have made it larger, doubt it would inflate costs much though. But even at 2.1x2.4m it is roomy enough for 2, just watch out for the counterweight shaft (ouch).