You'll need the following:

• 40 Wood Planks
• 15 Gold Bricks
• 15 Bellows
• 10 Anvils

While you can ask your friends for the Bellows and Wood Planks, you'll need to manually craft the Gold Bricks and Anvils, with each being complex crafting projects that will take you hours upon hours to complete. Or, you can purchase everything outright with Crowns, but isn't the entire point of this to earn a fourth workshop table for free?

Either way, once you've completed the fourth Workshop, it will function as all others do, giving you a chance to craft up to four items at once in your Kingdom, rather than just three. Hopefully, this will go over well enough with users that you'll see an increase in the capacity for other crafting buildings, like the Kitchen and Studio.