size(600,400);
float pad = 50.0;

// front face
rect(pad, 2*pad, width - 3*pad, height - 3*pad);

// top face
quad(pad, 2*pad, 2*pad, pad, width-pad, pad, width-2*pad, 2*pad);

// right face
quad(width-2*pad, 2*pad,
     width-pad, pad,
     width-pad, height-2*pad,
     width-2*pad, height-pad);