I started by selecting some of the faces on the bottom of the pieces of geometry and extruded them inwards to make a sort of dent that the feet can sit in. I then thought that maybe using a polygon sphere might work to create the feet, but I soon found it didn't have the type of geometry to make the type of shape I desired. So I deleted that and went for a polygon cube instead. I then adjusted, scaled, rotated and added resolution to the cube until I was happy with the outcome. I then duplicated and pushed them back, doing exactly the same thing as I did to the first bit of geometry; selecting faces, extruding upwards and adding the feet.