Rhino Grasshopper - Solid Surface Walkway

Main Topics
    Offsetting Curves
    Lofting
    Exploding a BREP
    Joining Curves
    Creating a solid surface

In this Grasshopper video series we will be re-creating the parametric walkway/bridge that had been done on the site before.  In this version of the exercise we'll create  the floor as solid rather than just a surface (i cheated last time :) ).  Since we don't have shelling (that I know of) in grasshopper I figured I would write a simple definition to do that for me.  After this video I will build out the rest of the walkway in a similar fashion to the previous video with a few new techniques along the way.  Please let me know if you would model this another way or if you have ideas for the rest of the walk way.