I recommend OSCS (kwdesigns) armor with knee/elbow foam inserts, resin detail plate and comm pad. Then add Steelblitz belt set, shoe details and straps (shoulder, elbow, knee). EVO3 makes a real nice Cody Episode III helmet. Those are what I consider to be the pieces of the best quality/price right now.
Once you have those, then you have to trim, assemble, putty and paint them.
You may have to do all the detail pieces on the Cody armor yourself, plus modify a pair of sneakers into proper clonetrooper shoes. There are no readily available shoes of any decent quality or accuracy, as far as I have seen.
I agree on everything in TK1536s post: The Clone Trooper costume will take you a whole lot of work to finish.