I bought mine. Seriously considered building one but was nervous about getting everything and it not working. Buying one "built" gave me peace of mind it would work. I didn't feel comfortable with a large outlay and then it not working. Now I'm also lucky enough to have a local place that ships fairly reasonably.
I also have of course upgraded since...

But that's much less intimidating then building a whole computer.
I have however built a PC for my daughter since then and it worked perfectly. So far, ironically, it's the most reliable PC we have.
I decided by that point that builduing was a good option as she already had a PC and nothing would be "down" whilst I troubleshooted etc if it came to that.
So my answer would be, "depends on your comfort level".
Build if you have the confidence to do so. It's not hard. Just a matter of matching components. All ya need is a case, PSU, Motherboard, RAM, GPU, sound card (optional), drives, fans etc.....and stick it all together. Usually motherboards come with enough instruction, it's quite simple if you pay attention.
In the case of my daughters', it didn't quite fire up first time. UH OH!! No biggie. Went through everything step by step in the instructions and found I had forgotten to connect one connector to the motherboard. Put it in place and........BINGO!!
I will say, it's quite satisfying the first time a PC YOU built fires up.
Anyways. If you feel comfortable. DO IIT! if you're nervous in any way, order one and maybe the next one you can build yourself.
I think basically, comfort level is the key.
I know we all love to say "I built it" but my PC Hector was bought and though I've torn the crap outa him since, I'm quite happy with my decision. It does what it's supposed to do and that's what counts.