Drawing an object in game to make it real.

I am not sure how to describe this I am trying to create a box that the player needs to interact with, I want to have the player draw inside the box and what they draw becomes a object in the world they can hold or interact with.

As an example they press the interact button a square pops up in front of them and when they draw a staircase and hit ok it spawns a staircase in front of them.