Here are some shots of my sister's kimono, made from some marbled cotton she had, showing really how basic it is. The most interesting shot I think is this one as it shows how the underlap/overlap rectangles are stitched to the centre front, then sliced down diagonally to the hip from the neck edge and how the neck piece is attached. Note at this stage the neck piece is two layers and quite wide, when it is flipped over and stitched down, as in the finished version, the band is four layers thick which helps it keep its shape. The woman I know who knew a lot about kimonos told me that this was typical.
I just stitch up the side seam and out to the sleeve, clipping at the underarm pivot. I have noticed in real kimonos that the intersecting seams at the underarm are often left open in sort of a vent/gusset. If none of this is clear please let me know and I will try to help. I am sure this is not an fully authentic method, but it looks enough like the real thing, and is so easy.