I started with a papercraft model of Claptrap. You can find the model here.
I used MATH to scale him up to a size that would fit into a suitcase. The challenge was the I would have to be able to assemble him in a hotel room.
I made templates out of card stock and cut the body pieces out of this plywood.
Most parts were epoxied and screwed together.
He got some yellow and black paint on the body.
I intended to make this a puppet that I could wheel around. I also wanted to be able to move his arms. I built shoulder and elbow joints to accomplish this.
I got a glowy ball at Wal-Mart for his eye. I used a PVC adapter to hold his eye. I found an old wheel for him to scoot around on. He got a few layers of acrylic and rub'n'buff for the details. As a bonus, I put a speaker in him and ran an the input from my phone to play sounds off a sound board.
Claptrap got a lot of love and I enjoyed pushing him around Dragon*Con.