I guess you need to decide if you are building an ROTJ, ESB or SE Boba and go from there. (PM sent) And THEN determine your budget and perhaps give yourself a pseudo timeline. From there you begin doing your research on who makes what - what each vendor's product looks like and if it meets your qualifications - and then begin purchasing what you cant make/fabricate yourself.
Some Fett's start with what we call the "soft parts" as it tends to be the first to put on items and are sometimes the more innexpensive parts. This would be:
The flightsuit
Neckseal
Gloves
Boot spats (rotj)
Boots
Honor sash
Cape
From there you can move up to bigger and badder parts.
I hope you get some responses from the more advanced players (Im still a noob)