It probably depends, no way to know what parts the stores or manufacturers (rebates) will have on black fri or cyber mon. It can be hit and miss though most of the more popular things typically have at least some sort of sale. I built a couple i5 systems during black fri/cyber mon of 2014 and got some decent deals. It took time sorting through things and dealing with rebates but was worth it. I saved more than enough to cover one of the i5 4690k's I picked up.
Another thing that helps is to get a feel for the current prices, prices fluctuate from month to month on various components anyway. Have a look at the cpu you're interested in, a couple of motherboards for it, a couple different gpu's then when the sales hit you'll know if it's a deal or not. For places/sites, it can pay to shop around. A couple years ago I ended up buying from newegg, amazon, ncixus and tigerdirect. Oddly enough I got my cpu cooler a month or so after the black fri sales, not much was on sale at that point and no major holiday sales. I ended up finding it for $55 instead of the usual $90 it goes for.
Sometimes it's just random and it worked out for me, I was in the market for a large air cooler to fit with a black theme. Had I not needed a cooler, been looking for an aio cooler or building a red or white themed pc it wouldn't have done me much good. Luck basically. The suggestion to use pcpartpicker is a good one, however if you see something you're interested in but it shows to be out of stock or unavailable it can be worth doing a further search for it. There are times pcpp lists something as 'out of stock' and I find it on newegg, amazon or elsewhere and it's available. Not always but sometimes.