I know very little about the EST3, but I would first caution you that you might be in over your head. To my knowledge, no hobbyist has ever set up a working EST3. It cannot be programmed without the SDU software and a license dongle, which you receive from taking a 5-day training course for $2400. I suppose you could also find an EST3-certified technician in your area who’s willing to help you out, but that’s unlikely. If want to buy a panel that you can actually use, I recommend reading So you want to buy a FACP...]this topic and considering a non-proprietary system.
That being said, if you’re determined to build one, the parts depend on what you want it to do. An EST3 consists of rail modules that mount to the rail chassis. Cabinets come in a variety of sizes that support anywhere from 5 to 21 rail modules. A basic EST3 panel requires a 3-CPU1 central processor, a 3-PPS/M primary power supply, and a 3-LCD display. You’d want at least one 3-SSDC Signature driver controller module, and the notification modules depend on what combination of NAC’s and/or audio circuits you want. See the http://firealarmresources.com/wp-content/uploads/2013/06/EST-EST3-v5.0-Installation-Service-Manual.pdf manual for more detail.