Most 3D Printing machines expect a file that represents one or more completely closed volumes, often described as “watertight.” Usually, the file format is a very refined mesh model, in a format such as STL. While simple to describe, it is often difficult to convert a 3D model of an architecture or infrastructure project into a watertight mesh. One of the challenges is creating an appropriately designed model for 3D printing. It is not just a matter of putting a fence around the data and sending it to the printer like a 2D line drawing; there are physical limitations to the rapid prototyping machine that need to be considered before the data can be printed. Creating printable data involves several factors that just cannot be controlled by any CAD software; it is up to the user to utilize build techniques based on the prototyping capability available. MicroStation offers several tools to make this process easier, but the key to getting good output is to supply good input.