No shame in doing something that already exists for yourself. But at this point I think it wouldn't be asked too much to just ask your favorite agent to check first if someone already implemented your idea in the past and then consider if your vision is really distinct enough to warrant anther instance of whatever you want to build.
Maybe that can happen through custom instructions. But I guess, by default the agent will happily do extra work and spend lots of tokens on “redundant” projects.
There is nothing particularly special about building something first.