The form of Design by Robert Frost?

Well, if I understand what you mean by "form," it's an Italian or Petrarchan Sonnet. This poem is organized into an octave (eight lines) and a sestet (six lines.) The octave's rhyme scheme is ABBAABBA and the sestet's rhyme scheme is CDCCDD. The Italian Sonnet usually poses a problem in the octave and a resolution in the sestet. This poem, however, simply states what is happening in the octave and poses a question and a possible answer in the sestet.