I too have made many of my own rulers... I use them all the time. If they are simple square or rectangle I cut them myself and have good luck doing that. I go to our plastics place here and pick up a few large pieces of "scrap" and cut my needed pieces from them. If I need a curved piece I have my husband cut it for me with his electric bandsaw. It's easy to buff the edges as well, just use very fine grit sandpaper and polish it carefully.
To make permanent markings on them I carefully align a metal rule excactly where I want it and use a scribe to make a scratch in the plastic... you have to be careful doing this as it is permanent... If you want to see that mark easily then simply go over the scratch with a fine tip sharpie.. Perfect rulers for pennies.