Of course several decisions have to be made before building an arcarde.
CRT or LCD? What sticks to use (analog, 4-way, 8-way)? what button layout? What kind of computing power etc etc.

Display

Probably one of the most passionate discussions is about the question CRT or LCD.
For me personally the answer was a LCD. I even choosed a 4k Display (HP 27q 3FV90AA 68,58 cm (27 Zoll) Monitor) as I intened to use per rom bezels, so I would not have to bother with black frames around the screen. And with enough computing power you can use a nice shader to recreate the look and feel of a CRT or another LCD (e.g. GameBoy or PSP). Surplus it saves space. The 4K display will also allow me to probably never have to change the monitor ever again, regardless of what kind of emulator comes up (Xbox One? PS4?).
However depending on your own personal focus a CRT might be a better solutions, this is up to you.

Control Panel

As I decided for a Kit the button layout was already set. 6 buttons plus 2 above each player. As buttons I choosed the Ultimarc Gold Leaf RGB buttons along with a PACLED64 controller.
Control sticks are Ultimarc Mag Stick Plus, they allow changing from 4-way to 8-way by pulling and twisting the lever. The automated alternative with a servo to switch the restrictor plate was too expensive for my (initial) budget.