From The Stargate Omnipedia
Antigravity dry dock
Station designed to serve as the construction platform for Goa'uld Ha'tak
vessels. A dry dock hovers over the surface of a world where a ship is being constructed, and is maintained by four antigravity emitters
beneath it. One such platform hovered over the Erebus
encampment, where slave Jaffa
were used for the construction of Ha'tak ships.
As naquadah is mined, processed and purified below, cargo ships transport the refined ore to the ship, where it is put to work in the immediate and continued construction of the vessel.
Orpheus - A Goa'uld antigravity dry dock remains several kilometers above the Erebus dig, until it is destroyed by two members of SG-1.