Take a look at Neyjour's gallery and you'll see that it is not a beginner's work.
Many people (me included) buy characters and start tweaking them afterwards to get a personal shape. Or combine/edit texturemaps.

Indeed, you can start from scratch, but sometimes it's more fun to start from something existing. You can go on foot to, say, Paris or you can take a plane and save your feet for the streets and boulevards of that city. And still decide your own parcours.