It's always a good time to build a PC. There's always going to be a new release from 1 of the CPU manufacturers, & at least 1 new line of GPUs from 1 of the GPU manufacturers.
The question is, a) what do you need the system to do, b) are you having any particular issues that make you think it's time to start over, & c) what are your current system's specs? If nothing else, you can always get suggestions on how to tweak/improve/upgrade your existing build without having to build a brand-new one from scratch.