People copy the "art" elements when making copies of Martin style guitars and don't think a thing of it. The more exact they can copy them the happier they are. I sometimes use commercially made rosettes on my instruments. It can save a lot of rather fiddly work and time I'd rather spend elsewhere.
The down side to buying premade parts is you can't claim it as your own work, and if taken to an extreme you might appear to be a "kit" builder.
One of the fun projects I have been doing lately is building cigar box ukuleles. Someone gave me a number of nice wooden cigar boxes to which I have been adding necks and fingerboards and bridges and tuners. The first couple I made all those parts, but looking online I found I could buy those parts cheaper than I could make them. The parts still require some modification and additional work but much of the work is done. So now I am more of an "assembler" who adds a few personal touches and less a "maker". It is still a fun project and they sound just as good, and require much less time to complete. I can say I "made" a cigar box uke, just not the "box" or the neck or the fingerboard or the bridge. And the cigar part went up in smoke long ago!
People will often ask if I made the rosette on an instrument, and I can sometimes answer "yes" and sometimes answer "no". Even the founder of the Martin guitar company often bought the lines and purfles for his instruments, and when he couldn't get them modified his production to use something he could get.
Personally I would say don't do it. It's one thing to come up with a design and then discover something very similar has been done before (any kind of creative/innovative work is a minefield of this these days), but when you had no idea such a glorious thing could exist until after you'd seen it, you just have to accept that the other guy is better than you, and go draw a bunch of mediocre junk in a futile attempt to catch up. Chances are someone else will be jealous of that mediocre junk and wonder why you're not satisfied with it... and then look at what you claim to be your greatest masterpiece and wonder why you're so satisfied with that mediocre junk 