Read up in the Props and Armor forum. There are a lot of options for materials, which changes how you will go about doing it.
Some common materials used to make mecha-type cosplays:
Each one has different methods and budget necessary to make your cosplay.
Within the Props and Armor section, there is a fairly new thread that will be very helpful to you. It's a tutorial with schematics on how to design and make a mecha/Gundam suit. I know yours is not Gundam, but many of the same things will apply for any robot/mecha type costume.
Some tips I'll add: Get a friend to be your "handler" while you wear your costume. If you plan to wear a mask or helmet, it will severely impair your vision and mobility. You will need someone to help you in crowds and be your eyes.
Less movement is better. In my personal experience, walking to the con and moving your limbs to pose will damage armor. I destroyed my boots just from walking from the hotel to the con. And my armor was all scratched up in places where the pieces rubbed together.
Costume Con - Kili in a dress
Atomic Lollipop - Come visit me at the Make-Your-Own-Button free craft booth!
Polar Chill - check out my costume DIY panel and workshop
FanExpo - Iron Man Mark VII version 2, Pacific Rim Jaeger pilot?
FanExpo - fem!Iron Man Mark VII - The Iron Man Armor Project
Atomic Lollipop - Vanellope von Schweetz; raver!Sailor Mars