clarify "extruder" vs "hot-end". I'm guessing by "extruder" you are referring to the extruder housing. There are many extruder housings on Thingiverse that work well. For all-metal hotends such as J-heads, E3D Lite6, V6, etc, the top of the hot-end remains cool - room temperature or cooler due to the cooling fan. For that application, a PLA printed extruder housing is fine.
Other hot-ends may produce too much heat at the top. Ubis and anUbis hot ends produce a lot of heat at the top. Any PLA extruder housing I've used with those hot-ends ultimately ends up warping and deforming over time.
For my direct extruder housing, I broke down and bought a metal Makrbot-style extruder housing and that has eliminated a lot of problems.