My favorite theme to build MOCs in is Castle. Here’s my blacksmith shop:
And here is the inside:
The shop contains quite a few sub builds that I use often, like the rack on the wall that holds weapons and tools, the sword holding stone by the door, and the anvil (which is just a modified version of the those seen in official sets). Though the whole MOC was a challenge to build, the roof was the trickiest part. I used SNOT (Studs Not On Top) to build the sides and used 2×1 bricks with a technic pegs clipped into technic holes to attach the main roof.
This is a black smith shop, so there is a window from which tools and weapons are sold.
Hope you enjoyed learning about how I built my blacksmith shop!