Studio Series Torso, arms and head Megatron
Lower body legs movie one megatron
Tank vehicle mode Studio Series Megatron
Backpack tank treads modified from the voyager rotf and dots shockwave.

After modifying the lower legs with the movie Megatron I went ahead and tried the wet wash paint with the acrylic pavement paint. I was impressed at how it turned out.

As for the tank mode, I took the rotf Megatron, popped the head off and left the tank mode. It took 3weeks to finally complete. I added some purple paint to give it a Decepticon color look.
As for the cannon, I used the Transformers Prime voyager Megatron cannon for the right arm and a flip out blade from the deluxe class Wreckage.
Shoulder spikes from voyager Megatron.

In addition, I added a gun barrel to give him a G1 cybertronian look.