The trouble with doing a miniature of Megatron is picking which version. Not because of the different ways he's been re-imagined: gun, tank, spaceship, dinosaur.
No, it's because of the different versions of his G1 robot form. Between the toy, the comic, and the cartoons, there's not much consistency between them. So, in the end, I settled on going with the cartoon version.
Colossus Heroclix for Megatron because I wanted a large build and a stern face. I added details with green stuff and added his fusion cannon and barrel using coffee stir sticks.
For his gun mode, I found marauderinc.com and picked up their G.I.Joe sized replica of Megatron's gun mode.
And just like in the cartoons, the size difference between his robot mode and gun mode is completely illogical.
So, in a way, it's accurate.