random extrude + offset

hi guys,

I obtain a crazy voronoi 2D on a plane and now I would to extrude this closed curves with a random form but in a range of 15 to 60 (centimeters).

plus, i would that this extrude forms are offsetted because I don't want that this volumes are in touch...a little distance just for render shadows and a best lookin' thing!

can you help me with an easy algorithm?

thanks a lot