Approx.700m (Lenght depends on the position of the arms. Model sized to match a Galaxy Class at the same scale )
Print orientation for Detail Plastic:
This is the McKinley Drydock as seen in TNG. This drydock is especially build to "hold" Galaxy Starships. In order to fit the ship in, the station can change its shape. The "arms" then can bend around the ship. The filming model only had 7 arms (just 3 big ones), most probably to get the Enterprise Studio model in it including the rig that keeps it in place. This model has 8 arms.
Contrary to my earlier assumption, it cannot hold Nebula Class ships, at least not if a pod is mounted on the back. The pod (any of them) would force the ship to sit so low inside the dock, that the large arms can not reach below the ship. The smaller arms on the rear would be useless too. Is seems that the large hinges on the rear structure are only there to let a Galaxy Class fly into it straight from behind, not to adapt to other ship classes.
Due to the fragile nature of the structure and because you might need to bend the arms a little when inserting a Galaxy Class miniature, i highly recommend buying this in Pa12 or Versatile Plastic. Detail Plastic might be too brittle for it.
If you need this in another material, size, or quantity, send me a message. I will try to make it as you need. Be sure to read my comments below my shop page