the tutorials below, authored and narrated by vera viana (11.2019), show examples on how to model the following polyhedra in rhinoceros:

the regular tetrahedron | the regular hexahedron | the regular octahedron | the regular dodecahedron | the regular icosahedron

REGULAR TETRAHEDRON

REGULAR HEXAHEDRON (CUBE)

rhino’s command box allows you to model a cube quite easily. Just select the tool, locate the point in which the cube is to be drawn (first corner or base), type the edge lenght, type enter for the width and enter again for the height. this will ensure that every edge lenght of the box is the same.