I think there are lot of discussions and examples on grasshopper forum.
http://www.grasshopper3d.com/photo/uneven-subdivision
http://www.grasshopper3d.com/photo/i-love-you
http://www.grasshopper3d.com/forum/topics/multiple-panelling-size-variation-based-on-text-lenght-and-height?xg_source=activity
Search, packing nesting, rectangle, uneven subdivision …
On your example I don’t understand how to fill 17 m with 6, 3, 1.5 ?
You could also use Substrate component from Grasshopper, but it will generate random rectangle. You will have to put angles to 0.