I wondered the same thing and last year ended up building up a system for a friend during Blackfriday/Cybermonday and yes the sales helped a lot.
RAM, SSDs, and PSUs had a pretty serious savings. The Intel CPU's I was looking at had an ok price break but no more than $20. Best thing would be to figure out your build now, and an alternate to parts (RAM choice 1 vs RAM choice 2) and then do the sales. Worst case, you dont get a sale price on the part you want. That is provided you can wait the few weeks to do it.
One thing I noticed on amazon last year was they didnt just have a normal sale, they had a rotating sale. Where somethings were only on sale for an hour or until items were bought up and they gave you a few hours notice on what was going up.