Thanks for all the kind words guys....
Well - all done!
Exterior/structure anyway - still need to route wiring, do some interior wall cladding and painting and carpet etc.... Then put the scope in!
Looking forward to set-up times of minutes over hours....
Some learning points -
* exterior ply - still make sure it is fully painted before any wet weather exposure
* don't paint late in the afternoon, especially if rain could be likely (der!)
* be careful how heavy you make a prefabricated part - especially if it needs to be carefully lifted 6 feet in the air!