I divided R2D2's body into 3 main differents parts that I would have to design : 

- the arms/legs (or whatever limb it is on a droid)

- the main body (which is basically just a cylinder)

- the head (which is basically half an empty sphere)

(plot twist : it wasn't that basic after all ... obviously ...)

Separately they were pretty easy to design. 

Those were the legs that i designed by drawing a simple sketch that I found resembling enough to R2D2, and then simply extruded them. 

I then managed to design its head by following a simple tutorial on Youtube. The idea was to create a sphere that would cut in half and then draw a sketch that you would extrude bu cutting through the other half of the sphere to create these patterns. 

For the main body, I simply created a cylinder.