http://th06.deviantart.net/fs70/PRE/f/2010/149/3/b/TFA_DEVASTATOR_3_of_3_by_digilaut.jpg I like this idea for this
Just a standard bulldozer, really. You can choose the vehicle modes, just based on what the robots look like.
What I mean is that it's easy to just make everything look like the movie characters, but original ideas is what will impress people. A lot of TF fan fiction just takes influence from the movies or TFP or Animated etc, but not a lot of them go their own direction with designs