From Star Ruler 2 Wiki
Sometimes you want to build a ship that build costs exceeds your actual and upcoming budget cycle. In such case a Drydock can be used to distribute build costs across several budget cycles.
To create a Drydock, simply doubleclick the desired ship at the planetary build screen. The Drydock will be created and will orbit around the planet you created it on. To continue with building, click the orbiting Drydock.