Building a PC for a newbie isn't the same as experienced, especially if their not mechanically inclined or have an interest in such. It could take a newbie 8 hours or days to get one up and running like it should be. Some people have issues understanding the BIOS or if they run into an error of sorts it may make for a frustrating experience. I remember my first PC, I had a bios error that meant I needed to make some changes to see my hard drive so that I could install windows. I posted on a forum like this to better understand and the response I got was "you should have gone out an purchased a prebuilt". Some similar responses resulted too. I'll never forget that. But luckily I was interested enough in tech that I wanted to learn...that part is very, very important.
I would recommend they have an interest in hardware/software first before bothering. Without interest it's a disaster waiting to happen. I would say to go look at either used gaming PC's or sites like Ibuypower and get a pre made system....plenty of affordable prebuilt PC's that are not much more cost than building yourself.