This is a fairly simple project. We wanted to build a K9 robot to put some hardware into at TinkerSoc, so I made some plans, first on paper, then in AutoCAD to laser cut slot together panels. It doesn't work perfectly, but it does work quite well.
The head should be attached to the body using PVC pipe in some sort of oversized rubber grommet (perhaps a gearstick cover?) and the whole thing needs spray painting silver. There is also a hole in the head for 2 8x8 dot matrix displays.
It cost ~£10 for the cutting and materials in our Architecture department at university, so it's a cheap project too!
We used 3mm mount board for our K9, you need to use something thin, or adjust the plans to take into account the width of the material, but provided it has some give and can be taped/glued into place it should be fine.
We have held ours together with sticky tape on the inside, but it seems strong enough, so it's not too much of a problem.
If you want to build your own, the AutoCAD plans can be downloaded from here.
Licensed as CC-BY-NC 3.0, 2013