Did you see a frame you like already?
Try to find one in this forum, hopefully a build component list will be available and make the process much easier for you.
Choose the right size.
Then come the troubles each time the frame connects something: the seatpost, the crankset, the fork and the rear wheel.
In general the frame builder provides a good enough carbon seatpost.
Otherwise just check the diameter is the same as the frame: 27.2mm, 31.6, etc.
The frame may come in various bottom bracket standards: PF30, BSA, BB30, BB86, BB386, etc.
That will influence what groupset you will be able to choose.
Then the headtube.
Chinese frames come generally tapered for 1.25"/1.5" forks.
Builders provide integrated headsets in general.
You can get some for $10 on Aliexpress too.
That will allow you to choose a fork.
Then the wheels.
You should go for thru axles. The frame builder provide sometimes a rear axle.
Unfortunately there are two standards now: 142x12mm and 148x12mm(boost).
If I were you I would go for the boost( frame and rear wheel ) but 142mm is still ok.
The hub of the rear wheel comes with a freehub body that is mainly Shimano 11sp(for NX or shimano cassettes) or Sram XD(for GX, XX1), be sure to choose the one that applies.
Start with this, and then you can look for a groupset, brakes, bar, tires, etc.