Masons line (typically nylon) has a tendency to stretch. Especially as it gets wet..the time you don't want the tarp to sag. Masons line can and will work till you can upgrade, but expect some sagging issues as the tarp is deployed. Many of us used masons line or paracord to start with.
If you can find some zing it, it is awesome as a rl.
30 ft. is more than adequate for most areas.