pYro_65:
Also place that line at the top of your sketch to declare the function ( or above its first use ).
Oh wow, I had no idea I had to declare a function before using it. You don't usually have to do that for functions - why for this one? For anyone else confused, I found more info on this here: http://www.cplusplus.com/doc/tutorial/functions2/ – scroll down to Declaring Functions.
Obviously these were just placeholders for the real code I'm building within these functions. I just couldn't get the build_simple function to even accept the StackArray object, so I simplified it for the sake of this post. I will start to put my real code in and see how it takes it. Thanks for the help!