How to modify G-code or a better place to get it I have built a 3D printer from salvaged/purchased parts. I am using an Arduino Uno and three easy driver stepper drivers with 3 CD-ROMs drives and a PC power unit. I ordered a 3D pen and have it mounted with a transistor to switch it on/off. Everything works but when I try to run code that I got from makercam.com it seems like it wants to fill in the shape rather than build up. 

I followed this tutorial YouTube - How To Make A Cheap 3D Printer and after modifying the G-code I am unable to get any successful prints.
Download an stl file from Thingiverse.com 

Put your .stl file in a slicer program like cura

It will output gcode for 3d objects rather than 2d.