Workshop is the place where you build and upgrade weapons.
After you unlock a blueprint you can build it in the workshop and you get the prototype weapon. This causes weapon to start appearing in Store and Slot Machine and in rewards after missions. Every weapon in game except defaults has it's blueprint number and after you build it, it appears in the slider on the right with wird "built". There are also some "Blueprint Not Found" slots even after you unlock them all, but that is a glitch and it is unknown when it will be fixed.
After you build any weapon, you get it in the Prototype form. Prototypes are level 0 and 1 weapons. You have option to not take them. They have very low price and they become useless after you reach higher levels.
You can upgrade each weapon to 5 stars. Upgrades are for 4 weapon stats: Impact, Fire Rate (RoF), Accuracy and Ammo. Last star drops the weapon for one level. Each stat can be upgraded only 1 time. The upgrade increases number near the weapon stat for a little. Sometimes upgrades will cause small effect, but they can also make the weapon extremely powerful. By upgrading RoF and Impact, you also increase weapon's DPS (Damage per second).
Upgrades cost a lot of money. Custom weapons are the most expensive to upgrade. Every time you try to upgrade a weapon you can success or fail. It is shown on the screen on the "upgrade machine" when you sucess or fail. Even when upgrade fails, it takes the same amount of money. As you upgrade the weapon more, chances for fail are increased. Sometimes if you fail, your weapon downgrades by 1 star unless it's not already upgraded.
Importrant note: The only way to use Level 31 weapon is to upgrade them to max so it drops one level to 30. This is NOT a bug
- The man in the workshop is an obvious reference to the Engineer from Team Fortress 2