Dave Everett's PDFs
Dave's plans are designed for styrene (mostly 3mm) this is the same plastic that Airfix and alike kits are moulded from.
It is sometimes called High Impact polystyrene (HIP) and is available in sheets up to 2.4m x 1.2m (8' x 4').
HIP is strong much stronger than MDF and is impervious to moisture, easy to cut, easy to join, easy to finish and a joy to paint.
Dave has also created a set of styrene plans for full-size R2D2 and R5D4 robots. he also wrote a tool and techniques booklet