During the Borg War Captain Cash took the USS Cario's saucer section into the Birar Patch to hide from the borg with a group of civilians he rescued from Qualor II before the Borg assimilated/destroyed the colony. Now the Cario's saucer section was kept in orbit of the Baku homeworld in the Briar Patch by Captain Cash while he watched for the Borg that he thought would come after him....he spent years repairing the saucer and keeping its power and weapons systems operational. So that saucer section is a habitable structure already in space.

By 2401 Starfleet's New Re-Exploration Iniative was well underway, with a few vessel's launched, the newly promoted Commodore Cash took his new command, USS Voyager NCC 74656-A back to the Briar Patch to help in creating Deep Space One. With another derelict saucer section, the Voyager crew with a engineers from the Starfleet Corps of Engineering where able to connect the two Galaxy class Saucers together. With a few more parts installed the station was operational for a crew to board.

Deep Space One is the first great space building project of the new century after the Borg War.
With resources at a minimum Starfleet Command decided on an unorthadox aproach to construction of a new outpost and formed the new Starbase into a usefull and habitable
outpost.