You can spend your Downtime to craft a single item following the rules in the Starfinder Core Rulebook (page 235 ). A character must use the skills listed in this section of the book and cannot use the Profession skill to craft equipment. It is assumed that between adventures, you have access to the tools and workshop necessary to craft equipment.
To craft an item, you must acquire the requisite number of UPBs. You can purchase UPBs at a rate of 1 UPB for every 1 credit spent. You cannot scavenge parts from equipment you own or collect during a Scenario. Equipment crafted between sessions is marked on the Chronicle Sheet.
If you have the Master Crafter feat, you receive a 5% discount on crafting if the crafted item is crafted using the Master Crafter feat’s associated skill. You may still craft only a single item during a single Downtime period.