With an outer diameter of only 3.5 meters, this is a very small observatory for a 62 cm telescope. The cinder blocks have a wide cross section, so the floor space is only around 9 square meters.
Unfortunately, I ran out of gravel yesterday. Three more tonnes will be delivered on April 4th. Then I can complete filling, levelling off, and compressing with a vibrating plate. I hope to complete the ground work during the weekend.