I create all my illustrations using collage, although I've recently started trying to mix a bit more drawing in with the paper. Here you can see a few different 'works in progress', from flat collages, to the 3D set I made for The Birthday Crown (Royal Collection Trust, 2016).
The images below take you from a colour rough to the finished 3D collage illustration (example from The Little Red Hen). This rough is a digitally coloured pencil drawing. It's followed by a couple of images showing how the separate collaged pieces are suspended from wires to create the 3D scene, then a photograph of the finished piece and, finally, the finished illustration with the wires edited out.