The most important thing is, what are you doing with them

It'll make for an interesting scenery peice

They are not all of the same cross section so I suppose it depends on how acurate you want to depict it, it also depends if you want it like the picture above or would be happy just going for a 'typical' representation?
You can get hex section styrene strip which would probably be your best bet for an all round solution, it could be heated to get the irregular curves shown in the picture above and can be chipped and beaten up a bit for a more irregular appearance.
For a more realistic look you could make each extrusion individually, keeping the cross section random and irregular, from clay and lay them over a former. Once dry, either oven or air they could be chipped etc.
Do show some photos when you are making it

cheers
James