I've cut them in strips, I started with a sheet of 60thou white plasticard, scored lines on the shiny side 10mm apart, lengthways, then scored lines on the matt side 16mm apart, crossways.
After it was all scored I used a fine wet and dry paper to remove any ridges from the scoring and also to scuff the surface a little.
Snapping the sheet along the 10mm score lines gave me 21ft of platform edging, about a third of what I need! Being in strips it should be fairly easy to get the edges even.
Once it is laid I will scribe the edge lines.
Andi