Google Sketchup is a fantastic tool to use for simple 3D design, and almost anyone can use it without after just a few minutes experimenting. Below are some links to tutorials that will get you started and familiar with Google Sketchup.
You can download the program from here: http://sketchup.google.com/download/
You can get mock up models here: Download
Word file on Aquaponics.
Do-it-yourself manual on how-to Aquaponics.
I've been trying to utilize Sketchup but it seems cumbersome. I've seen it recommended before. I just don't get it.