My daughter (Caitlin) inspects progress on the sarking. I used three layers of sarking to keep out heat - one wrpped around the outside of the building, and the other two with air spaces fixed between the studs. Heat build up is the main problem with a metal observatory; some tests show that it is generally 4 degrees cooler than the outside temperature on a hot day. Once the roof is rolled off it quickly equalises with the ambient temperature - the sarking has a low thermal mass and the plywood walls are poor heat conductors on the interior. Actually, I made a slight mistake here as all the sarking was supposed to be reflective side out.