You can check out the X-class website for a build list. There hasn't been much update though.
http://www.xclass.racing/products/ True X-class is 800mm+ frame. But there is a Beast Class drone that actually might gain more popularity. It uses all the same components as an X-class but in a more compact frame. See Joshua Bardwell video if you are interested.
Motors 4xxx-5xxx motors. 345-900kv. The good and relatively affordable MAD are impossible to find.
6s-12s+ lipos
ESCs - if you are running 12S, good luck finding anything descent. APD (Advance Power Device) is pretty much your only option. 6-8S is easier and have more options.
You will need a specific PDB. Matek and APD are the only two I know about.
VTX, camera and FC are standard.
If you check out my Criss Cross thread, I am stuck right now waiting to buy motors. There are some options, Brotherhobby, Xnova and T-motors. ZoeFPV has her BeeRotor motors. It is rated for 12S, but a crazy 950kv. I am worry there isn't enough torque. But these motors are affordable (relatively). I just haven't seen anyone talk about them.