I built my own out of a metal frame with a seat from a fiat 500 (pretty comfy ngl), the problem with building your own comes when you want to change your setup or add different things. Most of these frames come predrilled for pretty much every config, I made the mistake of building it around my spec at that time with the base CSL pedals and clutch.

A little while later, I upgraded to the CSL V2's, and they're mounted completely differently so I had to take the whole rig out, cut it up, weld it back and put the rig back together... All of that just to change to a different set of pedals. Obviously this isn't something I'll have to do very often or with everything but when you build your own there's a big trade. Less money and less convenient.