Sandbox games put the player in a similar situation. You now have the ability to shape the world and create beautiful things, but again there is the game world as a blank canvas looking back at you, wondering if you are going to suck as a creator again.
If you share this sandbox world with others, you may have already been exposed to all sort of wonderful creations. Maybe you have seen them on YouTube or Twitch. These people know how to build perfect columns, archways and vaults for their creations.
So you start placing a few blocks, but it gets you nowhere close to that grandiose design you had in mind. It is not that you lack the imagination. What you don't have is the technique to produce the elements you want.
We have designed a tool that can level the playing feel.
For a long time now we had architecture grammars. These grammars take a block of space and create something inside. I have shown many examples so far. Very often they were used to generate entire buildings. The trick is, you do not have to target full buildings for these grammars to be very useful.
You can realize your vision by combining simpler elements like roofs, barandas, columns, arches, vaults, etc. And these elements, instead of being labor intense, could be just the output of smart architecture grammars.
The fact that these are full fledged programs means they get to adapt to different configurations. For instance look at the output of this architecture program:
The program was clever enough to reinforce the corners. Yes, you could do this by hand, but imagine how many corners like this one you will get in your massive castle. Also note how the program has introduced a random element to the stone placement, making the walls more interesting.
Here is a video showing a different example:
As you can see the program adds more columns as they are needed. No distortion in the columns occurs as you make the box wider or taller.
At this point your are no longer dealing with the masonry. It is like you had hired one of the talented builders from YouTube to do the low level work for you. Knowing you have a repertoire of interesting prefabs you can combine in imaginative ways will surely help you get over your vacansopapurosophobia.