Leaders/polyleaders typically run from 1x too 1.5x rod length depending on the size of fly, presentation, conditions ect.
You can use both 10' or 14' polyleaders plus tippet, or tapered leaders in mono/fluro. Tapered mono leaders or floating PL's, can run up to 1.5x rod length, even a bit longer at times. At the shorter end of the spectrum, if you are using super fast sinking polyleaders and larger/heavier flys, a 10' PL with 3'-4' of tippet will give you more turn over power.