I think that’s too flat. There’s no easy place to put the width and suchlike. I think you’d want something like:

  (path (M 10 10 H 90 V 90 H 10 L 10 10) :color red)

Though probably I would prefer something more nested if possible, so you have a list of instructions rather than needing to parse them out of a flattened list. And I would likely use an alist rather than a plist for attributes like colour or stroke width.